Developmental pluripotency-associated 2 (Dppa2) gene is one of the genes recently identified to be expressed specifically in pluripotent cells. To investigate the role of Dppa2 in mouse embryonic stem (ES) cells, we examined its expression during differentiation and performed knockdown of Dppa2 in mouse ES cells. Our results showed that the expression of Dppa2 decreased markedly in differentiated cells. Dppa2 knockdown induced the differentiation of mouse ES cells, as indicated by reduced alkaline phosphatase activity, slightly downregulated expression of the putative pluripotency marker genes Oct4 and Nanog and increased expression of early differentiation marker genes, such as Fst and Psx1. Moreover, reduced expression of Dppa2 also repressed cell proliferation activity as shown by the 5-bromo-2-deoxyuridine incorporation assay. Hence, Dppa2 might play a role in maintenance of the undifferentiated state and proliferation of ES cells.