Chloasma, or melasma, is a commonly acquired pigmentary disorder among Asian women. It may be considered as a physiological change during pregnancy. The incidence in Asian women is higher than that in other ethnic groups but further epidemiologic data are needed. There are very few studies related to the benefits of sunscreens to prevent this dermatosis. The aim of this study was to assess the effectiveness of a broad-spectrum sunscreen in the prevention of melasma in Korean pregnant women. We tested the effectiveness and tolerance of a sunscreen product (SPF 50+, UVA-PF 30) during a 12-month clinical trial including 220 Korean parturients with skin type III and IV. 217 women completed the study. Only 3 (1%) of the study population developed melasma, which was mild (MASI grade between 1.2 and 2.7). In addition, the clinical effectiveness of the evaluated sunscreen was judged “good to excellent” by the majority of study participants and by the research dermatologists. The “excellent” tolerance of the sunscreen under evaluation was confirmed “good” to “excellent” in 95% and 97% of cases. This study clearly demonstrates that this broad-spectrum sunscreen is well tolerated and effective in the prevention of melasma in Korean pregnant women. Although treatment remains elusive, prevention is possible.