He said the woman was found floating in Lo Dalum Bay by a Myanmar worker on a boat, who notified police.
Her body has been taken to Koh Phi Phi Hospital.
Tanagon says a hospital examination revealed no signs of violence and the doctor ruled the cause of death as drowning.
It was believed the woman had been dead for about six hours before she was found.
"She was identified because the tour group contacted police after receiving news reports that the body of a foreign woman had been found. They then confirmed her identity through her tattoos," said Lt Tanagon.
The woman's family have been told he said.
Thai police are not releasing the woman's name.
A Ministry of Foreign Affairs and Trade spokesperson said the ministry was aware of the death of a New Zealand woman in Thailand and "is providing consular assistance to family".
