
Somchai was scheduled to leave Bangkok at 8pm for New Delhi where he will attend the summit on Thursday and Friday.
Thai Foreign Ministry's spokesman Thanee Thongpakdi said, "This summit will provide a good opportunity to review past cooperation and progress on a free trade agreement.
On Thursday, Thai PM is to meet his Indian counterpart Manmohan Singh before attending the smmit.
Bimstec comprises Bangladesh, Bhutan, India, Burma, Nepal, Sri Lanka and Thailand.