Metabotropic glutamate receptors (mGluRs) regulate the proliferation and differentiation of neural progenitor cells (NPCs) in brain; however, the mechanisms remain unknown. In this study, we investigated the effect of mGluR3 on the proliferation of human embryonic neural progenitor cells (NPCs), the expression of cyclin D1 and the activation of signaling pathways of mitogen-activated protein kinases (MAPKs). The results showed that mGluR3 agonist N-Acetylaspartylglutamate (NAAG) increased the proliferation of NPCs by increasing cell activity, diameter of neurospheres and cell division. In addition, mGluR3 siRNA decreased the NPC proliferation. The protein expressions of cyclin D1 increased with NAAG treatment and decreased after siRNA treatment. It was also found that activation of extracellular signal-regulated protein kinase (ERK) and c-Jun N-terminal protein kinase (JNK) signaling pathways were involved in the proliferation of NPCs. NAAG increased phosphorylation of ERK1/2 and JNK2 levels, and meanwhile p-p38 level decreased; but p-ERK1/2 and p-JNK2 levels decreased after siRNA treatment, and p-p38 level increased. ERK1/2 inhibitor U0126 and JNK2 inhibitor SP600125 attenuated the increase of proliferation induced by NAAG. These findings demonstrated that mGluR3 promoted the proliferation of human embryonic cortical NPCs and increased cyclin D1 expression by activating ERK1/2 and JNK2 signaling pathways in vitro, suggesting that mGluR3 may be a target molecule for regulating NPC proliferation in brain development.