Background: Prolonged use of low-dose estrogen ''20 micrograms or less" Combined oral contraceptive pill (that have estrogen and progesterone steroid hormone) had an effect on bone turnover .Bone mineral density is used in clinical medicine as an indirect indicator of osteoporosis and fracture risk. The aim of the study: The aim of this study was to investigate the effect of low dose oral contraceptive pill on the cortical thickness (in millimeter) and bone mineral density at the mandibular cortex of mental and gonial regions in Hounsfield unit(HU) using spiral computed tomography. Material and method: This prospective study was conducted on computed tomographic image of 100 women aged between (20-40) years .The collected sample includes patients attended for different diagnostic purposes to AL-Shaheed Al-Seder Teaching General Hospital of Al-Najaf AL-Ashraf from Julay, 2015 to May 2016.Data were grouped into two categories :group (1)control group (don't use combined oral contraceptive pill) (n=50);group(2)women taking low dose(20microgram) combined oral contraceptive pill for more than 2 years,(n=50).Cortical thickness measured in millimeter and Bone Mineral Density measured in Hounsfield unit both in mental foramen and gonial angle regions .Physical activity number of parity type of lactation were documented by questionnaire. Result: There was a statically significant difference; in cortical thickness p=0.037 and bone mineral density P=0.007 in mental area between the two groups ;the lowest mean in group (2)and highest mean in group(1) . After adjustment for age ,number of parity, and physical activity measurement scores ,there was a significant difference p=0.001 in mean of bone mineral density and p=0.065 for cortical thickness of gonial angle between the two groups ;the highest mean in group (1) and lowest mean in group (2). CONCLUSION: Computed tomography is a good diagnostic method to measure the value of cortical thickness and bone mineral density simultaneously in mental and gonial region of the mandible in premenopausal female using low dose combined oral contraceptive pill which have small effect on bone ;depended on the woman's age and the duration of using the pill ;that did not appear until about two years of use.