The suspects are identified as Thongchai Iamyong, Uam, Lachai and Awin. All except Thongchai were from Myanmar.
They reportedly had timber, several guns, ammunition and the head of a hornbill.
Police said they will investigate the case and take action against the four suspects.
The arrests took place during a joint operation by police and forestry officials, which started in the border province of Kanchanaburi on Tuesday.