To investigate the effect of polypeptide from Chlamys farreri (PCF) on NHDF in vitro, we modeled oxidative damage on normal human dermal fibroblasts (NHDF) exposed to ultraviolet B (UVB). In this study, 3-[4,5-Dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) and lactate dehydro-genase (LDH) were tested to measure cell viability. Enzymes including superoxide dismutase (SOD), glu-tathione peroxidase (GSH-PX), catalase (CAT) and xanthine oxidase (XOD) were determined biochemically. Total antioxidative capacity (T-AOC) and anti-superoxide anion capacity (A-SAC) were also determined. Ultrastructure of fibroblasts was observed under transmission electron microscope. The results showed that: UVB (1.176×10-4 J/cm2) suppressed the growth of fibroblasts and the introduction of PCF (0.25%-l%) before UVB reduced the suppression in a concentration-dependent manner. PCF could enhance the activities of SOD, GSH-PX and T-AOC as well as A-SAC. Also PCF could inhibit XOD activity, while it did not affect CAT activity. Ultrastructure of fibroblasts were damaged after UVB irradiation, concentration-dependent PCF reduced the destructive effect of UVB on cells. These results indicated that PCF can protect human dermal fibroblasts from being harmed by UVB irradiation via its antioxidant pro-erty. To investigate the effect of polypeptide from Chlamys farreri (PCF) on NHDF in vitro, we modeled oxidative damage on normal human dermal fibroblasts (NHDF) exposed to ultraviolet B (UVB). In this study, 3- [4,5-Dimethylthiazol- 2-yl] -2,5-diphenyltetrazolium bromide (MTT) and lactate dehydro-genase (LDH) were tested to measure cell viability. Enzymes including superoxide dismutase (SOD), glu- tathione peroxidase (GSH- PX), catalase Total antioxidant capacity (T-AOC) and anti-superoxide anion capacity (A-SAC) were also determined. Ultrastructure of fibroblasts was observed under transmission electron microscope. The results showed that: UVB (1.176 × 10-4 J / cm2) suppressed the growth of fibroblasts and the introduction of PCF (0.25% -l%) before UVB reduced the suppression in a concentration-dependent manner. PCF could enhance the activities of SOD, GSH-PX and T-AOC as well as A-SAC. Also PCF could inhibit XOD activity, while it d id not affect CAT activity. Ultrastructure of fibroblasts were damaged after UVB irradiation, concentration-dependent PCF reduced the destructive effect of UVB on cells. These results indicate that PCF can protect human dermal fibroblasts from being harmed by UVB irradiation via its antioxidant pro-erty .