Cyclin Y (CCNY) is a novel cyclin and almost nothing is known about its expression level and role in human cancers. In the present study, we found that lentivirus-mediated RNA interference (RNAi) of CCNY significantly downregulated its expression level. More importantly, knockdown of CCNY inhibited cell proliferation, colony formation, and cell cycle progression in glioma cells. These data suggest that CCNY might play an important role in glioma tumorigenisis.