This research aims to investigate the effects of clamping force on the behavior of steel gusset plates with slip-critical connection. Six specimens with two different materials are tested which three specimens are bolted with bearing-type connection and three specimens are bolted with slip-critical connection. The effects of number of bolts and material properties are investigated as the variable parameters of study. The results show that in the slip-critical bolted connections, the clamping force can increase the stiffness of connection in the small deformation zone. Also, this force increases the ultimate resistance of the tensile and shear areas that cause more resistant connection.