The night train from Bangkok goes to Surat Thani Hualumphong Station, where you can transfer to the ferry port for Samui, We recommend you take a sleeper carriage because the trains are very slow. Trains are normally fully booked so it’s advisable to book about three days in advance.
By far the cheapest mode of transport is the bus. From northern Thailand and Bangkok, head south for Surat Thani. These buses nearly always travel at night and there are different classes on offer. The best choice would be the Private VIP 24 seat buses, reclining seats and plenty of leg room. You can buy a ticket direct to Koh Samui with the price including the ferry. We recommend against buying tickets from travel agents in Khao San Road, please use a reputable agent. The journey from Bangkok to Surat Thani takes 10-12 hours. If you would like to sleep on the journey we recommend a sweater to combat the air-conditioning (VIP buses will provide blankets), and earplugs to combat the movie that will be playing through the night! This Bus will take you directly to the Seatran ferry pier at Donsak.
The bus from Phuket to Surat Thani is about 4 hours with regular departures. From Phuket you can also buy the ticket direct to Koh Samui.
If you want to experience the Thai way of travelling you could also try the local bus which will stop on route every time that someone along the roadside raises an arm. This mode of transport is only recommended if your budget is very small and if you have unlimited time. Once you arrive at the Bus station in Suratthani there are plenty of local taxi’s that can bring you to the Seatran ferry transfer bus.
The ferry from Donsak Port takes two and a half hours. It’s big and has seating and sunbathing areas. There is even an air-conditioned cabin. There is also a night ferry from Suratthani port that leaves at midnight and takes five to six hours.