Fyn-kinase is expressed widely in the entire brain, including the cerebellum. Fyn-kinase-deficient mice are known to exhibit hypersensitivity to ethanol. To evaluate the cerebellar functions of Fyn-kinase, we examined the dynamic characteristics of the horizontal optokinetic response (HOKR) and vestibulo-ocular reflex (HVOR) and its adaptability in Fyn-kinase-deficient mice. The HOKR was induced by sinusoidal oscillation of a checkered screen and the HVOR was induced by sinusoidal oscillation of a turntable in darkness. The HOKR gains of mutant mice were higher than those of the wild-type mice, and the HVOR phases of mutant mice were less advanced than those of the wild-type mice. However, no difference was noted in the adaptability of the HOKR induced by 1 h of sustained screen oscillation between the mutant and wild-type mice. The cerebellar functions appear to be unaffected by Fyn-kinase knockout.