The Hu proteins (the neuronal Elav-like: nElavl) are the mammalian homologue of Drosophila Elav, an RNA-binding protein expressed in the nervous system. In the embryonic brain, Hu family proteins (HuB/C/D) induce neuronal differentiation by binding preferentially to GU-rich sequences with secondary binding to AU-rich sequences in target RNAs. HuC is widely expressed in all types of neuron and is persistently expressed from early embryonic development to adulthood. To study the function of HuC in mature neurons, we generated HuC-deficient knockout (HuC KO) mice. At 7 months of age, HuC KO mice exhibited intention tremor, gait abnormality, and ataxia. Before the onset of these symptoms, the axons of Purkinje cells underwent morphological changes of swelling and retraction at the deep cerebellar nuclei, although the pathological changes were not observed during cerebellar development. Intriguingly, Purkinje cell soma seemed to be intact even at 21 months of age, and the number of the cells in HuC KO mice was the same as in their wild-type littermates. Histological analyses showed accumulation of mitochondria and amyloid precursor protein in the swollen Purkinje axons indicating that the axonal transport system might be impaired in HuC KO. To visualize mitochondrial dynamics in the axon, we infect Purkinje cells with a lentivirus encoding photoconvertible fluorescent protein KikGR that is targeted to the mitochondrion. Time lapse imaging of mitochondrial migration revealed disturbance of axonal transport in KO mice. Furthermore, to identify HuC targets in the adult cerebellum, we performed an RNA-binding protein immunoprecipitation-microarray assay and isolated several candidate RNAs, including Kinesin family members KIF3A and KIF3C, which are involved in axonal transport. Protein levels of KIF3A and 3C were significantly downregulated in KO mice; however, their transcript levels were normal. Overexpression of KIF3A or KIF3C in Purkinje cells derived from HuC KO partially rescued the swelling of axons. These results indicate that, at least in part, the pathophysiological mechanism of axonal degeneration in HuC KO mice is due to the down-regulation of the kinesin proteins.