Police were called to the temple at about 5pm after three monks walking by noticed a rotten smell and started investigating the source.
The monks found that the smell was coming from a black plastic bag under a bodhi tree about 50 metres from the multipurpose hall at the temple.
The bag had been torn open. Inside was the remains of a newborn girl, reported Kathu Police Chief Col Rungrit Ratanaphakdi.
The monks informed the abbot immediately, who organised for police to be notified, Col Rugnrit continued.
Forensic police and doctors from Vachira Phuket Hospital at the scene said that from initial inspections they were unable to determine the age of the newborn.
The remains would be taken for further medical examination, they confirmed.
Police said they would check CCTV at the temple in the hope of identifying and locating the person who left the remains at the temple.