Increasing evidence suggests that cytosolic non-specific dipeptidase 2 (CNDP2) appears to do more than just perform an enzymatic activity; it is functionally important in cancers as well. Here, we show that the expression of CNDP2 is commonly down-regulated in gastric cancer tissues. The ectopic expression of CNDP2 resulted in significant inhibition of cell proliferation, induction of cell apoptosis and cell cycle arrest, and suppressed gastric tumor growth in nude mice. We further revealed that the reintroduction of CNDP2 transcriptionally upregulated p38 and activated c-Jun NH2-terminal kinase (JNK), whereas the loss of CNDP2 increased the phosphorylation of extracellular signal-related kinase (ERK). These results suggest that CNDP2 acts as a functional tumor suppressor in gastric cancer via activation of the mitogen-activated protein kinase (MAPK) pathway.