The antioxidant activity of L-ascorbic acid is well established. Topical application of vitamin C has been shown to provide photoprotection, to decrease radiation damage and to prevent UV immunosuppression. L-ascorbic acid was found to stimulate collagen synthesis in monolayer fibroblast cultures and to enhance the hydration of the stratum corneum, as well. The magnesium salt of ascorbyl-2-phosphate (MAP) is a stable derivative of ascorbic acid, which was found to be equivalent to ascorbic acid in stimulating collagen synthesis in monolayer fibroblast cultures. Furthermore, the epidermal transportation and conversion of MAP to L-ascorbic acid has been proved in humans, as well. Although several studies strongly support the idea that ascorbic acid enhances the hydration of stratum corneum, the hydrating properties of MAP have not been examined yet. In this study, tests were carried out in a half face, double blind manner consisting of 28 days usage (twice daily applications). According to our findings the presence of MAP compared to placebo, caused low improvement in the hydration of the skin or the concentration of moisturizing raw materials in the placebo masked its moisturizing property.