Flavonoids are one of the major components found in the peels of citrus fruits. Present evidence has suggested that polymethoxyflavonoids, including nobiletin and tangeretin isolated from Citrus sunki, have many biological properties, such as anti-inflammatory, anti-oxidant, and anti-obesity capabilities.Here, we investigated the effect of Citrus sunki peel extract and its possible mechanisms on oxidative stress-induced MMP-1 expression, a major marker of skin photoaging. H2O2 induced MMP-1 expression in a dose-and time-dependent manner. Extract of Citrus sunki peel (1-25 μg/ml) dose-dependently decreased MMP-1 mRNA levels. When H2O2 was combined with Citrus sunki peel extract, the phosphorylation of ERK was further decreased compared to a single treatment with H2O2 alone. Moreover, U0216, an MEK inhibitor, markedly prevented the production of MMP-1. These data suggest that Citrus sunki peel extract has demonstrated protective activity against oxidative damage on MMP-1 expression, and ERK MAP kinase may be involved.