They were working on a 1.8-metre deep and 50-metre long ditch at a house under construction on Sathit Yuthitham Road.
Two of the workers were pronounced dead when they arrived at hospital, after the 1.30pm accident.
Muang Satun superintendant Pol Colonel Phumsit Nawang said police would investigate the cause of the collapse and would ask the construction company to pay compensations to the dead and wounded.