Kwanchai Sarakham, also know as Kwanchai Praipana, leader of the Love Udon Club, was seriously wounded in a hail of gunfire into his residence on Jan 22.
He has been hospitalised at Rama 9 Hospital in Bangkok after being transferred from an Udon Thani hospital.
The four suspects were accompanied by a military judge advocate to Udon Thani police station to acknowledge the charges.
They were identified as M/Sgt Mavin Yangbua,38, M/Sgt Viroj Pimsingh, 36, 2nd Lt Pratya Chanrodpai, 40 and Sgt Chanond Tabtimthong, 30.
The first three were attached to the 19th Cavalry Division, Surasee Camp, in Kanchanaburi, while the fourth suspect worked at the 9th Infantry Division.
They denied all charges as witnesses were invited to identify them.
M/Sgt Mavin and M/Sgt Viroj were bailed out with Bt450,000 bond each while Lt Pratya and Sgt Chanond posted bond at Bt500,000 and Bt100,000 respectively.
Police said the four men would be in army custody while police prepared to submit evidence and witnesses against them to the Attorney General.
Police continued their manhunt for two other suspects who remain at large.