A 3-D linear analysis of rotating stall is carried out to clarify the effects of spanwise distribution of cascade characteristics. An actuator disk model of annular cascade is employed. A linear spanwise distribution of the performance slope is considered to examine the effects of the threedimensionality in the cascade characteristics. Many characteristic solutions were found corresponding to various kinds of radial mode. It was found that the 0th order radial mode is more unstable than higher order modes. It was also found that uneven spanwise cascade characteristics distribution makes the 0th mode more unstable, and alters the 0th order mode so that the amplitude of the disturbance becomes larger at radial locations where the positive slope of the performance is larger.