Anniversary events were held at Kamala Memorial Stone, Mai Khao Memorial Wall, Phuket City Hall and Patong Beach in the southern resort island of Phuket.
Interfaith ceremonies were also held in resort towns across the Andaman coast from Phang Nga province to Phi Phi archipelago.
Many relatives from abroad who lost their loved ones in the December 26, 2004 tsunami travelled to Thailand to join the service.
The tsunami struck during peak tourist season at the beaches and islands in Thailand, killing thousands of holidaymakers as well as workers and villagers.
Thailand was one the countries hit by the tidal waves from a 9.1-magnitude earthquake off the coast of Indonesia's Sumatra island. The disaster claimed an estimated 230,000 lives, mostly in Indonesia.
It was the deadliest tsunami in recorded history.
DPA