HMG-CoA reductase inhibitor (statin) induces skeletal muscle injury including myalgia, myositis and rhabdomyolysis. The mechanism of this myotoxicity remains unknown. We examined the effect of statins on single skeletal myofibers enzymatically isolated from rat flexor digitorum brevis muscles. Fluvastatin or pravastatin induced numerous vacuoles in the myofibers on the 3rd day of statin-application in the culture medium. This effect progressed in a time- and concentration-dependent manner followed by cell death on the 5th day. The electron micrographs revealed craters of various sizes along the salcolemma, the swellings of the sarcoplasmic reticula, and mitochondria, in addition to the intracelllar vacuoles. When caffaine was introduced to the myofibers at the 72 hours of fluvastatin treatment, the induced cell-shortening was smaller than that of the control and prominent blebs were the formed on the surface of the myofibers, which were not observed in the control fibers. The co-application of geranylgeranylpyrophosphate (GGPP) completely cancelled the morphological changes while farnesylpyrophosphate (FPP) was ineffective. Furthermore, perillyl alcohol, a selective Rab geranylgeranyl transferase inhibitor, mimicked the effect of statins, while a specific geranylgeranyl transferase-I inhibitor, GGTI-298 or a farnesyl transferase inhibitor, FTI-277 failed to do so. Exoenzyme C3, Y27632, or wortmannin did not mimic the statin effect. In addition, the satellite cells and fibroblasts also injured by fluvastatin. GGPP attenuated the damage in both of cells, however FPP was only able to prevent injury in the fibroblasts. These results suggest that Rab GTPase inactivation is therefore a crucial factor in statin-induced-morphological abnormalities in skeletal muscle fibers, and that these morphological changes were accompanied by a vulnerability to the contraction in skeletal myofibers.