Bangkok Airways plans to launch a daily service between Koh Samui and Kuala Lumpur on 31 March.
The airline will be operating an Airbus A319 on the route, said an official.
Schedules in Innovata show Bangkok Airways will be the only operator on the route.
In addition, Finnair started code sharing with Bangkok Airways on 15 January.
The airline placed its code on Bangkok Airways' services from Bangkok to Chiang Mai and Phuket, and from Koh Samui to Bangkok, Hong Kong and Singapore, Finnair said in a statement.