PURPOSE: The purpose of this study was to analyze the differences of bone density and structure after immobilization prior aerobic exercise and resistance exercise. METHODS: Twenty four mice were randomly divided into 3 groups: CC: 4weeks control cage after 2weeks immobolization (n=7), RT: 4weeks resistance training after 2 weeks immobilization (n=7), AE: 4 weeks aerobic training after 2 weeks immobilization (n=7). The prior exercise was performed aerobic and resistance exercise. The body weight, muscle weight, and bone morphometric microstructure parameter including bone mineral density (BMD), bone specific surface (BS/BV), percent bone volume (BV/TV), trabecular thickness (Tb/Th), trabecular number (Tb/N), trabecular separation (Tb/Sp), structure model index (SMI), connectivity density, and cross-sectional area was evaluated using by microcomputed tomography (micro-CT). One-way repeated ANOVA was used to evaluate the differences between three groups and paired t-test analysis was applied to examine the different between immobilization leg and non-immobilization leg. RESULTS: The results of this study indicated that the body weight was increased after 4 weeks, and decreased after 2 weeks immobilization. The gastronemius and soleus muscle weight was significantly decreased in immobilization leg compared to non-immobilization leg. BMD, BV/TV, BS/BV, Tb/Th, Tb/N, Tb/Sp, and Cross-sectional area in immobilization leg of CC was lower than immobilization leg of RT and AE. CONCLUSIONS: These results suggest that 4 weeks prior exercise might improve the bone density and microstructure, even though 2 weeks immobilization. Especially, the prior resistance exercise has more beneficial effects on muscle weight, bone density and microstructure.