Objective:To investigate the relationship between serum level of Apelin-13 and bone mineral density (BMD) as well as other parameters, and determine the influence of Apelin-13 on osteoporosis in patients with Type-2 diabetes mellitus.Methods:Seventy-six patients with Type-2 diabetes mellitus were recruited from Department of Endocrinology of our hospital between January 2013 and July2017. The clinical data, including age, gender, height, weight, body mass index (BMI) and disease duration were recorded for all patients. Blood sample was collected for measurement of Apelin-13, Procollagen type-I N propeptide (PINP) and Cross-linked carboxy terminal telopeptide of type-I collagen (ICTP), and BMD was tested with a dual-energy X-ray absorptiometry scanner.Results:The patients were divided into three groups, in which 19 patients were assigned in osteoporosis group, 25 in osteopenia group and 32 in normal group. The level of Apelin-13 in osteoporosis group was significantly lower than that in osteopenia and normal groups (p<0.05), and the value in osteopenia group was significant lower than that in normal group (p<0.05). Correlation analysis showed in the included patients the level of Apelin-13 was positively correlated to the value of BMD and PINP (p<0.05), but negatively correlated to age and ICTP (p<0.05).Conclusion:In conclusion, this study demonstrated that there was a close relationship among Apelin-13, BMD, ICTP and PINP, and Apelin-13 plays an important role in the occurrence of osteoporosis in patients with Type-2 diabetes mellitus.