The Department of National Parks, Wildlife and Plant Conservation denied on Saturday that the name of Koh Tachai would be changed to "Sirivannavari".
Department chief Niphon Chotibal said that the name of the island off Thai Muang district in Phangnga province remained the same.
He issued the clarification one day after Jeerasak Chookwamdee, director-general of the Fifth Conservation Area Administration Office in Nakhon Si Thammarat province, said that HRH Princess Sirivannavari Nariratana had renamed the island after being impressed by its white sandy beaches and crystal-clear water.
The princess has given the island, which forms part of the Similan Islands, "Sirivannavari".
Mr Niphon said that the princess had visited Tachai and other islands from March 22-26 for a nature field trip as she was interested studying marine and coastal resources.
The island derived its name from a local resident called "Tachai" who first discovered it.