The PC12 is the widely used cell line to study neuronal differentiation. We had extensively investigated the details of protein expression in differentiated PC12 cells by proteomic analysis. The cells were incubated at the presence of nerve growth factor. We had analyzed the expression changes in the differentiating PC12 cells by 2-dimensional electrophoresis and the identification of the proteins using MALDI-TOF MS. By comparing expression pattern in the time course, we identified the candidate genes which are associated with neuronal differentiation. Among these genes, we performed real-time PCR analysis to validate $Idh3{alpha}$ expression by the time course. To identify the function of $Idh3{alpha}$ in neuronal differentiation stage, the transfection of $Idh3{alpha}$ to PC12 cells was performed. As a result, we proved that up-regulation of $Idh3{alpha}$ causes reduction in neural differentiation of PC12 cells. Based on these data, we suggest that $Idh3{alpha}$ plays a role to the neuronal differentiation.