Background: Atopic dermatitis (AD) is related to a deficiency of delta-6-desaturase, an enzyme responsible for converting linoleic acid to gamma-linolenic acid (GLA). Evening primrose oil (EPO) as a source of GLA has been of interest in the management of AD. Objectives: The aim of this randomized, double blinded, placebo-controlled clinical study is to evaluate the efficacy and safety of EPO in Korean patients with AD. Methods: 50 AD patients were enrolled for the study and randomly divided into two groups. The first group received an oval unmarked capsule containing 450 mg of EPO (40 mg of GLA) per capsule, while placebo capsules identical in appearance and containing 450 mg of soybean oil were given to the other group. Treatment continued for a period of four months. The Eczema Area Severity Index (EASI) scores, transepidermal water loss (TEWL), and skin hydration were evaluated in all the AD patients at the baseline, and in months 1, 2, 3, and 4 of the study. Results: At the end of month 4, the patients of the EPO group showed a significant improvement in the EASI score (p = 0.040), whereas the patients of the placebo group did not. There was a significant difference in the EASI score between the EPO and placebo groups (p = 0.001). Although not statistically significant, the TEWL and skin hydration also improved in the EPO patients group. Conclusion: We suggest that EPO is a safe and effective medicine for Korean patients with mild AD.