Proliferation of pancreatic stellate cells (PSCs) plays a cardinal role during fibrosis development. Therefore, the suppression of PSC growth represents a therapeutic option for the treatment of pancreatic fibrosis. It has been shown that up-regulation of the enzyme heme oxygenase-1 (HO-1) could exert antiproliferative effects on PSCs, but no information is available on the possible role of carbon monoxide (CO), a catalytic byproduct of the HO metabolism, in this process. In the present study, we have examined the effect of CO releasing molecule-2 (CORM-2) liberated CO on PSC proliferation and have elucidated the mechanisms involved. Using primary rat PSCs, we found that CORM-2 inhibited PSC proliferation at nontoxic concentrations by arresting cells at the G(0)/G(1) phase of the cell cycle. This effect was associated with activation of p38 mitogen-activated protein kinase (MAPK) signaling, induction of HO-1 protein, and up-regulation of the cell cycle inhibitor p21(Waf1/Cip1). The p38 MAPK inhibitor 4-(4-flurophenyl)-2-(4-methylsulfinylphenyl)-5-(4-pyridyl)imidazole (SB203580) abolished the inhibitory effect of CORM-2 on PSC proliferation and prevented both CORM-2-induced HO-1 and p21(Waf1/Cip1) up-regulation. Treatment with tin protoporphyrin IX, an HO inhibitor, or transfection of HO-1 small interfering RNA abolished the inductive effect of CORM-2 on p21(Waf1/Cip1) and reversed the suppressive effect of CORM-2 on PSC growth. The ability of CORM-2 to induce cell cycle arrest was abrogated in p21(Waf1/Cip1)-silenced cells. Taken together, our results suggest that CORM-2 inhibits PSC proliferation by activation of the p38/HO-1 pathway. These findings may indicate a therapeutic potential of CO carriers in the treatment of pancreatic fibrosis.