Phytocomponent p-hydroxycinnamic acid (HCA) has been shown to have stimulatory effects on bone calcification and inhibitory effects on bone resorption in rat femoral tissues in vitro. Whether HCA has a stimulatory effect on mineralization in osteoblastic cells is unknown. This study was undertaken to determine the effect of HCA on mineralization in osteoblastic MC3T3-E1 cells in vitro. Cells were cultured for 72 h in a minimum essential medium (alpha-MEM) containing 10% fetal bovine serum (FBS), and the cells with subconfluency were changed to a medium containing either vehicle or HCA (10(-7)-10(-5) M) without FBS. Culture with HCA (10(-7)-10(-5) M) did not have a significant effect on cell proliferation and cell death. Deoxyribonucleic acid (DNA) content in osteoblastic cells was significantly increased after culture with HCA (10(-6) or 10(-5) M) for 48 or 72 h. Alkaline phosphatase activity in osteoblastic cells was significantly increased after culture with HCA (10(-7)-10(-5) M) for 24, 48, or 72 h. The results with Alizarin red staining for calcium showed that mineralization was significantly stimulated after culture with HCA (10(-8)-10(-5) M) for 7, 14, or 21 days. This study demonstrates that HCA has stimulatory effects on mineralization in osteoblastic MC3T3-E1 cells.