Vietnam and Cambodia are pretty close and the two countries share 3 international border crossings.
There are many tourists in Cambodia from Vietnam and vice versa. And among all the cities of Cambodia, Phnom Penh and Siem Reap are the two cites that people from Vietnam tend to visit most.
Phnom Penh is the capital and the largest city in Cambodia. It is also a famous destination to the tourists for many traveling attractions. While Siem Reap is another famous tourist city of Cambodia with also a lot of well-known travel sites.
Although the distant between the two countries is close, the transportation is somehow complicated and time-consuming. There are different ways either overland or by plane to travel between Vietnam and Cambodia, not only by plane like the most of other countries. Unfortunately, there is no train to travel between Ho Chi Minh and Cambodia.
And obviously, you need a tourist visa to travel between the two countries. Somehow you can get it at the airport when travelling by plane but you’d better to prepare it in advance.
Following are the detailed information about the transportation from Phnom Penh to Ho Chi Minh City.

Transportation from Phnom Penh to Ho Chi Minh city
The following are some ways to get from Phnom Penh to Ho Chi Minh city:

From Phnom Penh to Ho Chi Minh city by Bus

This is definitely a straightforward, cheap and comfortable way to get from Phnom Penh to Ho Chi Minh. And it is also most recommended among tourists.
Buses from Phnom Penh to Ho Chi Minh take average 6 hours. The ticket price is from $6 to $12.
Most of buses from Phnom Penh to Ho Chi Minh are convenient with air-conditioner, toilet, free water, snack, moist tissues, wifi (not fast all the time). Some buses have an attendant who gives you an overview about the trip, she/he is also the one who goes around and collects passengers’ passport. When meeting a river along the journey, buses will across by a ferry. Buses depart and arrive in the center of the two cities without directly without bus changing. However; there are some stops for food, facilities using and at the border for border crossing process, then you will be returned your passport with the exit stamp.
Bus tickets are available online so you can easily book the ticket yourselves through some simply steps like choosing the bus line, ticket prices then trip schedules, using your smart phones, laptop or tablet. The number of the seat will be written in your ticket. Or you ask your guesthouse, hotel for help and more information.

There verified bus companies providing buses from Ho Chi Minh to Phnom Penh but the most outstanding are Giant Ibis and Mekong Express.
Giant Ibis: This is always an outstanding choice when you travel between the two cities by bus.
Add: near the night market in central Phnom Penh
Price ticket: $18
Giant Ibis provide buses from Phnom Penh to Ho Chi Minh departing at 8:00, 12:00 pm
Tourists get off at their station at Riverfront (Sisowath Quay).
Mekong Express:
Add: near the Olympic Stadium
Price ticket: $14
Mekong Express provides not only the normal bus but van (minibus) which is little faster.
Buses from Phnom Penh to Ho Chi Minh depart at 7:00, 8:30 and 14:00
Minibuses from Phnom Penh to Ho Chi Minh depart at: 6:30 and 15:30

From Phnom Penh to Ho Chi Minh city by Boat

If you don’t want to travel from Phnom Penh to Ho Chi Minh City by the normal way, you can try another more challenging but more fantastic one, it is by boat. You will take a boat from Phnom Penh to Chau Doc (Vietnam) or then take a bus from Chau Doc to Ho Chi Minh. The price will be from $19 to $50, depending on the level of the boat you choose
If you want to get off at Chau Doc, then you can take a boat of Hang Chau company. The ticket price is $28.60 for adult, free for children under 4 and half of a price for children from 4 to 8. The daily boat from Phom Penh to Chau Doc of this company departs at 12:30 pm at Number 103, Sisowath, SK Phnom, Kh Daun Penh, Phnom Penh, Cambodia. It takes 1 hour for formalities and another 3.5 hour to get to Chau Doc. There are also different kinds of boats for charter (07 seats, 13 seats, 22 seats, 25 seats) from Hang Chau for you to hire if you want to travel to Ho Chi Minh by a private boat. You can get more information from their website: hangchautourist.vn or contact with +85-512932346.
If you don’t want to travel directly and cheap, there are luxury cruises providing trips in 2-3 days and the price is obviously high, the price is from $1,000 and depends on the levels and the seasons. Heritage Line is one of the companies providing such tours. The downstream cruise departs at Phnom Penh and goes through the Crossing Boarder and Tan Chau in the first day, in the second day it goes through Tan Chau, My An Hung and Sa Dec, in the third day it goes through Binh Thanh Island, Cai Be, My Tho and finally arrives at Ho Chi Minh City in the last day. For more information, you contact sales@asiajourneytravel.com, or contact hotline number +84969303322

From Phnom Penh to Ho Chi Minh city by Plane

This is the fastest but the most expensive way to travel from Phnom Penh to HO CHI MINH. The planes take flight from Phnom Penh International Airport (Phnom Penh) to Tan Son Nhat International Airport (Ho Chi Minh).
The flights take about 50 minutes from Phnom Penh International Airport to Tan Son Nhat International Airport. You have to spend 15 minutes more for transferring, 3 hours before departure completing the checking procedures. The drive from the Tan Son Nhat International Airport to the city center takes you another 20 minutes.
The average ticket price is $100. The cheapest one-way ticket is Vietjet Air’s. The other airlines having the flights from Ho Chi Minh to Phnom Penh are Qatar Airway, Vietnam Airlines, China Easter.