OBJECTIVES: In the past decade many studies established relationship between vitamin D deficiency and chronic musculoskeletal pain including low back pain. Present study aimed to examine the effect of vitamin D3 supplementation in patients with chronic low back pain with low level of vitamin D. METHODS: This single arm, open label study was conducted in a public tertiary care teaching hospital in India after obtaining approval from the Ethics Review Board of the hospital. Adult patients of either gender, aged 18 to 65 years, with a diagnosis of CLBP and low serum 25(OH)D3 levels (<30 ng/mL) and not responding to medications and physical therapies, having a pain score of at least 50 as assessed on 0 – 100 Visual Analogue scale (VAS) at baseline were eligible for study recruitment. Cholecalciferol (active vitamin D3) in a dose of 60,000 IU/week for a period of 8 weeks was given to the enrolled subjects according to standard guidelines. Study endpoints include change in pain score and disability as measured by modified Oswestry disability questionnaire (MODQ). Patient information and outcome measures were collected at baseline, 2, 3 and 6 months.  RESULTS: A total of 68 chronic low back patients were included in the trial. Mean baseline vitamin D level is found to be 12.80+5.73 ng/ml. After treatment it significantly (P<0.01) increased to 36.07+12.51. VAS (81.03+18.57) and MODQ (44.83+15.47) were high at baseline. Pain intensity has significantly reduced to 44.71+18.96 (<0.05) and 35.74+17.75 (<0.05) at 3 and 6 months respectively. Disability has significantly reduced to 30.94+12.48 (<0.05) and 26.10+10.03 (<0.05) at 3 and 6 months respectively. CONCLUSIONS: Present study shows that vitamin D supplementation can improve the pain and disability in patients with CLBP. Study results should be carefully interpreted as it is a single arm open label study and concomitant medication usage was not assessed.