Background: Vitamin C is known to both inhibit melanin formation and reduce oxidized melanin. However, vitamin C does not easily penetrate the skin. In this study, vitamin C iontophoresis was employed in order to enhance vitamin C penetration. Objective: The purpose of this study was to evaluate the efficacy of vitamin C iontophoresis for melasma patients. Methods: Twenty-nine females with melasma were enrolled. For iontophoresis, a vitamin C solution was applied to one side of the face, while distilled water was applied to the other side as a control. The L (luminance) value was measured by a colorimeter to obtain an objective pigmentation parameter. Results: Twelve weeks after iontophoresis, the colorimeter of the treated site showed a significant decrease in the L value (from 4.60 to 2.78, p = 0.002), compared to that of the control site (from 4.45 to 3.87, p = 0.142). Conclusion: Vitamin C iontophoresis may be an effective treatment modality for melasma.