An investigation of the speed effect, i.e., the effects of centrifugal force and coriolis force, on the mode localization of a mistuned blade-disk is presented in this paper. A disk comprising of periodically shrouded blades is used to simulate the weakly coupled periodic structure. Galerkin method is employed to derive the mode localization equations of the mistuned system with the consideration of coriolis force. The blades are approximated as cantilever beams, and five axial and lateral modes of each blade are used to present the dynamic behavior of the system. Ten modal coordinates have been considered for each blade. The effects of coriolis force and the magnitude of disorder on the localization phenomenon of a rotating blade-disk system were investigated numerically. Numerical results obtained herein indicate that the coriolis force may enhance the localization phenomenon.