Excitatory stimuli are known to be a potent regulator for induction of neuronal differentiation. Calbindin-D28K buffers intracellular Ca2+ and modifies synaptic functions in neurons. However, the effects of calbindin-D28K on the regulation of activity-induced neuronal differentiation and related biochemical modifications remain unsolved. In the present study, by a gain-of-function study with retroviral vector system and dicer-generated small interfering RNA (d-siRNA) to effectively knock down the expression of calbindin-D28K, we demonstrated that calbindin-D28K at a physiologically relevant level promoted neuronal differentiation and neurite outgrowth. Increase of neuronal differentiation by calbindin-D28K overexpression was concurrent with the expression of basic helix-loop-helix (bHLH) transcriptional factors, phosphorylation of calcium and calmodulin-dependent protein kinase II (CaMKII) and NeuroD at Ser(336). KN-62, a highly specific CaMKII inhibitor, blocked the up-regulation of proneural bHLH genes, p-CaMKII, and pSer(336)NeuroD. Calbindin-D28K appeared to facilitate neuronal differentiation of both fetal and adult hippocampal progenitor cells. Together, these findings establish the novel calbindin-regulated function of CaMKII and NeuroD in control of neuronal differentiation and neurite outgrowth.