Abstract: In the current study, the effect of shot-peening on the static torsional strength of AA7178-T6 was investigated. Time of shot-peening was adopted as a varied parameter to evaluate its effect on plastic state in static torsion test of alloy. Residual stresses and surface roughness was measured to indicate the influence of shot-peening time on alloy surface state. Torque predicted was calculated to evaluate the elastic torque and plastic torque values according to shot-peening parameter. The results show that the shear strain decreases whenever shot-peening time increase especially when up to 30 min that shear strain reduced by 45% and plastic torque predicted also decreased at this time by 10% compare to its values of specimen without peened which means that the strength of alloy improved with this process while shear stress decreased by 3.84% at this condition. The total torque predicted was closed to experimental torque with average variation 14%. Experimental torque decreased by 3.84% with the increasing of shot-peening time.