Background: Probably related to immune dysfunction, psoriasis vulgaris is a chronic, painful, disfiguring and disabling dermatological disease, carrying an increased risk of serious comorbidities. Current conventional therapies can be costly, show risks of side effects and have limited efficacy, with relapse common on treatment cessation. Chinese herbal medicine is effective in treating psoriasis vulgaris. However, any benefit of adding Chinese herbal medicine to conventional treatments when treating psoriasis vulgaris is yet to be determined. Methods/design: This is a pilot randomized, placebo controlled, double-blinded trial. The pilot is primarily to determine the feasibility of undertaking a full size randomized trial. Thirty participants with psoriasis vulgaris and Psoriasis Area Severity Index (PASI) scores >= 7 and <= 12 will be included. Participants will be randomized (in a 1:1 ratio) to receive oral granulated Chinese herbal medicine YXBCM01 plus topical calcipotriol 0.005% or oral YXBCM01 placebo plus topical calcipotriol 0.005% treatment for 12 weeks, with a 12-week follow-up phase. The Chinese herbal medicine or placebo will be administered orally as dissolvable granules. The primary outcome measure will be PASI change (%) from baseline to the end of treatment phase. Secondary outcomes will include safety, key psoriasis-related cytokine changes (for example, IL12, IL17 and IL 23) during the entire trial and symptom relapse rates at the end of the follow-up phase. Discussion: The study will evaluate the feasibility of a randomized controlled trial investigating combined conventional and Chinese herbal medicine therapy for psoriasis vulgaris. The ingredients of YXBCM01 were selected based on literature, the expert opinion on herbal medicine and pre-clinical evidence, for instance Chinese herbal medicine possesses anti-inflammatory or antiproliferative properties.