Primarily through in vitro studies, the Rho-family of small GTPases and their effector proteins have been implicated in mediating oncogenic properties of cancer cells. We sought to determine if pharmacological inhibition of the RhoA effector proteins known as Rho-kinases (ROCK) with the small molecule inhibitor Y-27632 could inhibit melanoma in vitro and in vivo. We demonstrate that Y-27632 treatment of a panel of melanoma cells alters cellular morphology leading to spindly cells with decreased lamellipodia and increased filopodia formation. Y-27632 treatment decreases invasion and alters cell survival of cultured melanoma cells. IP injection of Y-27632 in tumor-bearing mice resulted in a reduction in melanoma tumor volume compared to control treated mice. These findings suggest that ROCK inhibition can reduce melanoma tumorigenicity.