p38 mitogen-activated protein kinase (MAPK) regulates matrix metalloproteinase-1 (MMP-1) gene expression bidirectionally depending on the induction. We sought to determine whether cytokines related to the regulation of extracellular matrix could activate p38 MAPK in dermal fibroblasts. We determined p38 MAPK phosphorylation/activation in dermal fibroblasts stimulated with platelet-derived growth factor-BB (PDGF-BB), transforming growth factor-β or interleukin-4. Induction of MMP-1 mRNA by PDGF-BB was enhanced in the presence of a specific inhibitor of p38 MAPK, suggesting that p38 MAPK would function as a negative regulator of the MMP-1 mRNA level. We then determined which isoforms of p38 MAPK expressed in dermal fibroblasts were responsible for the downregulation of the MMP-1 mRNA level. Overexpression of p38β2, but not of p38α, significantly decreased PDGF-BB-induced MMP-1 promoter activity, although PDGF-BB activated signaling pathways to both p38α and p38β2. Taken together, the results of this study indicate that p38β2 can function as a negative regulator of MMP-1 induced by PDGF-BB in vitro, suggesting that activation of p38β2 might contribute to the pathogenesis of cutaneous fibrosis.