An unidentified body was found floating in the Chao Phraya River in Bangkok's Bang Kho Laem district at noon on Thursday, police said.
Bang Kho Laem police were alerted at 12pm that a body was trapped in floating weeds near the Bang Kho Laem pier.
A team of rescue workers from the Portecktueng Foundation and a doctor from the Siriraj Hospital were dispatched.
The man appeared to be around 40 to 50 and was about 165cm tall. He was wearing a black T-shirt with a Samsung logo.
No wounds and documents were found on him. The doctor said he died about 48 hours earlier.
The body was sent for a post-mortem at the Siriraj Hospital.