Bill Clinton and George Bush Sr have been asked by the White House to raise funds to help those affected by the deadly wall of water last December.
They are starting their tour with a visit to the small village of Baan Nam Khem, just north of Phuket.
The Americans will later continue to visit affected communities in Indonesia, Sri Lanka and the Maldives.
The former US leaders arrived in Phuket shortly after 1200 (0500 GMT) and were greeted by Thai Foreign Minister Surakiart Sathirathai.
“I just want to see what’s being done, thank people, see what else we can do,” said Mr Clinton as the pair arrived in the Thai resort of Phuket.
