Police said the accident happened on a road in Ban Nai Toon village in Tambon Na Reng.
The big bike driver, Amornrat Klaothanom, 34, a resident of Nakhon Si Thammarat’s Tha Sala district, was killed outright.
A 14-year-old girl, Parita Dokbua-ai, who was riding in the sidecar of an oncoming motorcycle, also died at the scene.
Another girl, Phattarawadee Chubutr, 14, was rushed to the Tha Sala Hospital along with her relative, who was driving the bike with the sidecar. The driver was not named by police.
Police theorized from traces on the road that the big bike was driving at a fast speed and the driver lost control before crashing into the sidecar.