Abstract Objective We aimed to measure the serum level of vitamin k2 in postmenopausal osteoporotic patients to determine its role in the disease. Patients and Methods Our study was designed as a cross sectional study, with 15 postmenopausal osteoporotic patients (with reduced bone mineral density BMD), aged between 54-58 years old compared to 15 healthy controls (with normal BMD at all of lumbar spine, femoral neck and hip) matched in age with the patients. All participants were subjected to full medical history taking, physical examination and functional assessment of the activity of daily livings (ADL). Biochemical assays of thyroid stimulating hormone, parathyroid hormone, total calcium, phosphorus, alkaline phosphatase (ALP), 25-hydroxyvitamin D (25 (OH) D), erythrocyte sedimentation rate, Kidney and liver function tests and serum levels of vitamin k2 were performed. Results The patients showed highly significantly lower vitamin k2 levels (P < 0.05) and non-significant correlations between vitamin k2 and the activity of daily living (ADL) nor the other laboratory assessment parameters (P > 0.05) among the patient’s group. Conclusion Vitamin K deficiency is highly prevalent in the majority of our patients and should be considered an associating factor in the etiology of postmenopausal osteoporosis. Vitamin k2 deficiency could result in a decrease in the bone mineral density in postmenopausal women, so vitamin k2 levels should be checked in post-menopausal osteoporosis and any deficiency must be treated and corrected to improve the bone mineral density.