Abstract: Based on the theoretical study of a rigid flat punch acting on an elastic half-space,a face-on-face torsional friction model of glass fiber reinforced monomer casting nylon (MC nylon) against 45^# steel was built. In addition, their tribological behavior was studied to validate the model.The results indicate that the shape of T-θ curves varied from linear, elliptical into quasi-parallelogram curves with increasing angular displacement. Torsional contact interface of MC nylon filled with 0%, 3% and 5% glass fiber was gross slip regimes, correspondingly under their torsional angular displacement of 0.5°, 1° and 2°. Friction coefficient directly influenced the variation of adhesion radius as a function of torsional angle, i.e. it resulted in different torsional interfacial contact regimes. The torsional torque of MC nylon composite underwent a sharp decrease to stable state with increasing torsional angle. From the above-mentioned relationship, the torque of torsional contact under partial slip was higher than that under gross slip. Good agreement between the calculated torque and experimental torque was found under different angular displacements,which indicated the torsional friction model could approximately predict the torque of MC nylon composite.