BACKGROUND: Despite the vitamin D treatment in patients with multiple sclerosis (MS), there continues to be controversial discrepancy in outcomes according to the current research. Many systematic reviews have evaluated the effect of vitamin D as an adjuvant treatment in patients with MS; however, there is no consensus on the optimum administration time and dosage of vitamin D intake. A meta-analysis for exploring the different administration time and dosage of vitamin D is warranted. METHODS: Randomized controlled trials (RCTs) on the effect of different administration time and dosage of vitamin D in patients with MS were recorded within 7 databases. This meta-analysis was performed with 2 clinical outcomes: EDSS (Expanded Disability Status Scale) and relapses during research. RESULTS: The pooled results indicated that receiving different administration time and dosage of vitamin D as an adjuvant treatment had no significant therapeutic effect on MS according to the EDSS scores and relapses during research. CONCLUSION: According to our meta-analysis, the administration of vitamin D in different dosages (ranging from 2,857 to 14,007 IU/day) and treatment period (ranging from 6 to 24 months) did not affect the clinical outcomes (EDSS and relapses during research) in patients with MS. Additional RCTs should be conducted to explore whether a longer duration and a larger dosage of vitamin D without serious adverse effects might produce therapeutic effects in patients with MS.