Background. There are limited randomized controlled trials of oral vitamin D supplementation in psoriasis, especially in Asia, and the results are inconclusive. Objective. To investigate the clinical effect of oral vitamin D supplementation on psoriasis. Methods. Patients with psoriasis were randomized to receive vitamin D2 60,000 IU or similar-looking placebo pills once every 2 weeks for 6 months. The primary outcome was improvement of the Psoriasis Area and Severity Index (PASI) score at 3 and 6 months after treatment. Serum levels of 25(OH)D, calcium, phosphate, parathyroid hormone, and C-reactive protein and adverse events were monitored. The chi-square test, Fisher’s exact test, Student’s t-test, and Spearman’s correlation analysis were used in statistical analysis. Results. Of 50 subjects screened, 45 were eligible and randomized to the oral vitamin D2 group