Chloasma (melasma), an acquired hypermelanosis, is often recalcitrant to various treatments and an amenable, as well as safe, pigment‐reducing modality is needed. We investigated that the reducing effect of proanthocyanidin, a powerful antioxidant, on chloasma in a one‐year open design study. Proanthocyanidin‐rich grape seed extract (GSE) was orally administered to 12 Japanese woman candidates with chloasma for 6 months between August 2001 and January 2002 and to 11 of these 12 for 5 months between March and July 2002. Clinical observation, L* value (lightening) and melanin index, and size (length and width) measurements of chloasma were performed throughout the study period. The first 6 months of GSE intake improved or slightly improved chloasma in 10 of the 12 women (83%, p < 0.01) and following 5 months of intake improved or slightly improved chloasma in 6 of the 11 candidates (54%, p < 0.01). L* values also increased after GSE intake (57.8 ± 2.5 at the start vs 59.3 ± 2.3 at 6 months and 58.7 ± 2.5 at the end of study). Melanin‐index significantly decreased after 6 months of the intake (0.025 ± 0.005 at the start vs 0.019 ± 0.004 at 6 months) ( p < 0.01), and also decreased at the end of study (0.021 ± 0.005) ( p < 0.05). GSE is effective in reducing the hyperpigmentation of women with chloasma. The beneficial effects of GSE was maximally achieved after 6 months and these was no further improvement after this period. The latter GSE intake for 5 months may prevent chloasma from becoming worse prior to the summer season. GSE is safe and useful for improving chloasma. Copyright © 2004 John Wiley & Sons, Ltd.