The indie drama also won best screenplay - which also went to Assarat - best cinematography and best art direction.
A love story set in a small Thai town after the 2004 tsumani, the film has already won several festival awards, including a Tiger Award at Rotterdam, and was picked up for international sales by Momento Films.
Meanwhile, Nonzee Nimibutr's pirate action adventure Queens Of Langkasuka picked up three awards at the Thai ceremony, including best visual effects, best sound and best costume design.
The best actor prize went to Ananda Everingham for romantic comedy Happy Birthday, while Ratchawin Wongviriya won best actress for her role in love triangle drama The Last Moment.
Sorapong Chatreepicked up thebest supporting actor award forplaying the mentor of Tony Jaa's character in Ong Bak 2. Best supporting actress went to Focus Jeerakul for her role in teenage ensemble drama Hormones.
The awards, organised by the Federation of National Film Associations of Thailand, were held at the Thailand Cultural Centre in Bangkok.
FULL LIST OF WINNERS:
Best picture: Wonderful Town (prods: Soros Sukhum, Jetnipith Teerakulchanyut)
Best director: Aditya Assarat - Wonderful Town
Best actor: Ananda Everingham - Happy Birthday
Best actress: Ratchawin Wongviriya - The Last Moment
Best supporting actor: Sorapong Chatree - Ong-Bak 2
Best supporting actress: Focus Jeerakul - Hormones
Best screenplay: Aditya Assarat - Wonderful Town
Best visual effects: Queens Of Langkasuka
Best editing: 4Bia
Best cinematography: Wonderful Town
Best song: Jab Mue Chan by Kongdej Jaturanrasamee (Handle Me With Care)
Best original score: The 8th Day
Best sound: Queens Of Langkasuka
Best art direction: Wonderful Town
Best costume design: Queens Of Langkasuka
Best make-up: The 8th Day
Lifetime Achievement Award: Dome Sukwong - Thailand National Film Archive