Background: Background: Chronic LBP was defined as pain in the small of the back for a minimum of 5 days per week for at least 3 months. Those who reported no LBP or who reported experiencing occasional non-persistent LBP that occurred no more than twice per week were classified as having no LBP. Aim: The aim of the study is to Association of chronic low back pain with the Vitamin D and bone mineral density. Methods: this was a cross-sectional observational study. A total of 120 patients of chronic low back pain were included in our study. The level of 25(OH) D (vitamin D) in serum was measured by chemiluminescent immunoassay methodology. Result: Out of 120 enrolled participants 24 (20%) were males and 96 (80%) were females. Mean age was 32.80 ± 8.7 years. The duration of low back pain ranged from 7 to 14 months with a mean of 11.05 ± 4.31 months. Spine BMD on DXA scan ranged from 0.90 to 0.98 g/cm2 with a mean of 0.95 ± 0.02.The mean BMD decreased significantly with increasing age and severity of LBP; 20-30 years vs. 31-40 years (0.94 ± 0.01 vs. 0.93 ± 0.02; p=0.001).There was no significant difference in mean BMD across various durations of low back pain; 7-10 vs. 11-14 months (0.92 ± 0.03 vs. 0.91 ± 0.01; p=0.48). Majority of the chronic low pain patients (40%) associated with the vitamin d deficiency. Conclusion: The mean BMD at spine was found to be low in patients with CLBP. It was significantly lower in older patients and those with severe low back pain. However, it didn’t change significantly with various durations of low back pain or gender. Keywords: Chronic low back pain, bone mineral density, Vitamin D.