Objective To study the changes of biochemistry indexes in blood serum and bone mineral density (BMD) of secondary osteoporosis after spinal cord injury (SCI) in rats. Methods 120 male Wistar rats were divided randomly into 12 groups (n=10). The rats in control groups were only removed larmina with dura intact, without spinal cord injury at the level of the tenth thoracic vertebrae, the rats in experimental groups were also removed larmina, then paraplegic model was made by the method of Allen's (60gcm). The changes of biochemistry indexes in blood serum and BMD were observed. Results Compared with control groups, the concentrations of alkaline phophatase (ALP) were decreased at the 1st and the 3rd week in experimental groups (P0.05). BMD of tibia was decreased at the 7th and 11th week in experimental group (P