Collapsin response mediator protein 5 (CRMP5) is one of the CRMP members that expresses abundantly in the developing brain. To examine the in vivo function of CRMP5, we generated crmp5-deficient (crmp5(-/-)) mice. Anti-calbindin immunofluorescence studies of crmp5(-/-) mice revealed aberrant dendrite morphology; specifically, a decrease in the size of soma and diameter of primary dendrite of the cerebellar Purkinje cells at postnatal day 21 (P21) and P28, but not at P14. Coincidentally, CRMP5 is detected in Purkinje cells at P21 and P28 from crmp5(+/-) mice. In cerebellar slices of crmp5(-/-) mice, the induction of long-term depression of excitatory synaptic transmission between parallel fibers and Purkinje cells was deficient. Given that brain-derived neurotrophic factor (BDNF) plays major roles in dendritic development, we tried to elucidate the possible roles of CRMP5 in BDNF signaling. The effect of BDNF to induce dendritic branching was markedly attenuated in cultured crmp5(-/-) neurons. Furthermore, CRMP5 was tyrosine phosphorylated when coexpressed with neurotrophic tyrosine kinase receptor type 2 (TrkB), a receptor for BDNF, in HEK293T cells. These findings suggest that CRMP5 is involved in the development, maintenance and synaptic plasticity of Purkinje cells.