Statins are widely prescribed drugs in cardiovascular diseases. Recent studies also demonstrated anti-inflammatory and immunomodulatory properties of statins by modulating the activity of small GTPases. Statins are thus considered as potential therapeutic drug for the inflammatory demyelinating disease multiple sclerosis (MS). However, little is known about the effects of statins on myelin-forming oligodendrocytes. Here, we show that statins hamper process and myelin formation in vitro by interfering with Ras and Rho signaling in mature oligodendrocytes and provide evidence that statins impair ongoing remyelination in vivo. Our findings may have significant implications for the application of statins in MS patients and in other demyelinating diseases of the CNS.