Neuropilin-1 (NRP-1) is a non-tyrosine kinase receptor for vascular endothelial growth factor (VEGF) that was recently found to play a role in tumor functions. Previous studies demonstrated that NRP-1 was overexpressed in a number of human tumors, including glioblastoma (GBM). However, the role of NRP-1 in glioma progression has yet to be adequately elucidated. Thus, we examined the expression of NRP-1 in human glioma cell lines using Western blotting, and cell cycle distribution and proliferation by transfection of the U373 cell line with NRP-1 short interference RNA (siRNA). Results showed NRP-1 siRNA to significantly reduce NRP-1 gene expression, decrease in vitro cell proliferation and induce cell apoptosis in cultured glioma cells, along with the accumulation of cells in the G1 phase and a decrease in cells in the S phase. Our results further revealed that NRP-1 knockdown decreased the expression levels of Bcl-2 family proteins and deactivated extracellular signal-regulated kinase (ERK) and c-Jun-N-terminal kinase (JNK)/mitogen-activated protein kinase (MAPK) signaling pathways, closely associated with cancer progression. Thus, our results provide a molecular mechanism for the effect of NRP-1 in tumors, rendering NRP-1 an attractive candidate as a therapeutic target in certain types of cancer, such as GBM.