Rosmarinic acid is known to have anti-inflammatory and immunomodulatory activities. This study was performed to evaluate the effect of rosmarinic acid on atopic dermatitis (AD), one of the inflammatory disorders of the skin. Twenty-one subjects (14 women and seven men, 5–28 years of age) with mild AD participated in this study. Rosmarinic acid (0.3%) emulsion was topically applied to the elbow flexures of AD patients twice a day (once in the morning and once in the evening). All subjects were evaluated for skin conditions before treatment at the first visit, and then at 4 and 8 weeks after treatment. According to local Severity Scoring of Atopic Dermatitis index results, erythema on antecubital fossa was significantly reduced at 4 and 8 weeks (P < 0.05). Transepidermal water loss of the antecubital fossa was significantly reduced at 8 weeks compared to before treatment (P < 0.05). The results from self-questionnaires on the efficacy of rosmarinic acid indicated that dryness, pruritus and general AD symptoms improved. Our investigation into the AD-mitigating effect of rosmarinic acid through in vivo experiments demonstrated the possible clinical use of rosmarinic acid as a therapeutic agent for AD.