The effect of varying microstructures of Mo films on CIGS preferred orientation has been studied by changing Mo working pressure (in sputtering). CIGS I(220)/I(112) and IGS I(300)/I(006) have strong dependencies of the residual stress of Mo closely related to its microstructures: they increases with Mo pressure and then gradually decreases with Mo pressure, as the residual stress does. The trend is exactly opposite to the known effect due to Na. Thus this work shows that Mo microstructure itself can determine IGS and CIGS textures without assistance of other factors such as Na. XRD analysis on selenized Mo and TEM work on IGS/Mo show that MoSe2 reactivity itself influences the IGS texture more than its orientation. In addition, MoSe 2 reactivity depends on the in-grain density of Mo which is linearly related to the residual stress.