Hochu-ekki-to is a traditional herbal (Kampo) medicine that has been shown to be effective for patients with Kikyo (delicate, easily fatigable, or hypersensitive) constitution. Previous case reports have suggested that this herbal drug was effective for a certain subgroup of patients with atopic dermatitis (AD). We aimed to evaluate the efficacy and safety of Hochu-ekki-to in the long-term management of Kikyo patients with AD. In this multicenter, double blind, randomized, placebo-controlled study, 91 Kikyo patients with AD were enrolled. Kikyo condition was evaluated by a questionnaire scoring system. All patients continued their ordinary treatments (topical steroids, topical tacrolimus, emollients or oral antihistamines) before and after their protocol entry. Hochu-ekki-to or placebo was orally administered twice daily for 24 weeks. The skin severity scores, total equivalent amount (TEA) of topical agents used for AD treatment, prominent efficacy (cases with skin severity score = 0 at the end of the study) rate and aggravated rate (more than 50% increase of TEA of topical agents from the beginning of the study) were monitored and evaluated. Seventy-seven out of 91 enrolled patients completed the 24-week treatment course (Hochu-ekki-to: n = 37, placebo: n = 40). The TEA of topical agents (steroids and/or tacrolimus) was significantly (P < 0.05) lower in the Hochu-ekki-to group than in the placebo group, although the overall skin severity scores were not statistically different. The prominent efficacy rate was 19% (7 of 37) in the Hochu-ekki-to group and 5% (2 of 40) in the placebo group (P = 0.06). The aggravated rate was significantly (P < 0.05) lower in the Hochu-ekki-to group (3%; 1 of 37) than in the placebo group (18%; 7 of 39). Only mild adverse events such as nausea and diarrhea were noted in both groups without statistical difference. This placebo-controlled study demonstrates that Hochu-ekki-to is a useful adjunct to conventional treatments for AD patients with Kikyo constitution. Use of Hochu-ekki-to significantly reduces the dose of topical steroids and/or tacrolimus used for AD treatment without aggravating AD.