Introduction: Vitamin D has a significant role to play in bone metabolism and neuromuscularfunction. Several researchers have indicated that Vitamin D deficiency may be possiblyrelated to musculoskeletal pain including chronic low back pain. Aim: We aimed to examine the relationship between the levels of vitamin D and patients with chronic low back pain and to investigate its effects on pain and functional capacity. Materials and Methods: Two hundred and sixty patients (Female/Male:110/150) with complains of low back pain for more than three months, aged between 18 to 60 years and both genders, participated in the study. Visual Analog Pain Scale (VAS) was used to measure the state of pain. Pain-related functional capacity was evaluated using Modified Oswestry Disability Questionnaire (MODQ). Patients were classified into three groups based on their serum vitamin D levels: Sufficient ( 30 ng/mL), insufficient (20.1-29.9 ng/mL) and deficient ( 20 ng/mL).