Background: Stress fracture is a fracture that occurs in the repetition period, when the load is given during exercise without adequate rest. One of the factors in stress fractures is bone density in individuals. The incidence of stress fracture in the military population can be estimated at between 4 - 7% in male sex. In 2016 at the Selopamioro Yogyakarta State Police School there were 9 stress fracture events from 239 students, this incidence increased by around 80% from the previous year, which was as many as 5 events. Aim: To know low bone density can increase the incidence of stress fractures in the Selopamioro Yogyakarta State Police School and to find out the bone density difference with calcium supplementation with vitamin D. Method: This research method is quantitative research with observational analytic research method with cross sectional approach on 36 students of Selopamioro Yogyakarta State Police School consist of 18 students in class 2016 and 18 students in class 2017. Data were collected from student medical record data. Data were analyzed using Fisher‟s test to see the difference in low bone density rates with the incidence of stress fracture and using a paired sample t-test to see the difference in bone density rates with calcium supplementation with vitamin D. Result: There is a difference between low bone mineral density and an increase in the incidence of stress fractures but it is not statistically significant (p> 0.05). Student bone density after calcium supplementation with vitamin D, the osteoporosis category became osteopenia by 3 (75%) and osteoporosis became normal by 1 (25%). The results of the number of students with osteopenia to normal is 3 (25%). There are differences in bone density rates with calcium supplementation with vitamin D (p <0.05). Conclusion: Stress fractures in osteopenia are greater than the number of stress fractures in normal people. Providing calcium supplements with vitamin D increases bone density and reduces the incidence of stress fractures compared to students without calcium supplements with vitamin D.