The purpose of this study was to investigate the effects of combined resistance training and aerobic training with protein intake after resistance training on body composition in obese middle-aged women. The subjects were 42 middle-aged women (age : 56.5±4.3 years, BMI : 26.6±2.3 kg/m²), who were classified into three supplementation groups: Protein group (PG), Isocalorie placebo group (IG), and Noncalorie placebo group (CG) by Double Blind Randomized Trial. The training program consisted of combined resistance training and aerobic training for 10 weeks, 5 times per week: twice a week in a university training room and 3 times per week at home. The subjects took the nutrient supplement immediately after each resistance training session. We measured body weight (Bw), body fat volume (Bf) by bioelectrical impedance analysis (BIA), and cross-sectional area (CSA) of muscle of the thigh extensor group (Te), flexor group (Tf), and psoas major (Pm) by magnetic resonance imaging (MRI) before and after the 10-week training period. Irrespective of group, Bw and Bf showed a significant decrease after the training period compared to before (p<0.001), and the CSA of Te muscle showed a significant increase after the training period (p<0.01). Moreover, the interaction of time×group was accepted in the CSA of Pm muscle (p<0.05), and the increase in muscle volume for PG was the highest increase among the three supplementation groups (p<0.05)(PG : 2.1±0.8 cm², IG : 1.3±1.0 cm², CG : 1.3±0.9 cm²). These results suggest that combined training in middle-aged obese women improves body composition, and resistance training with protein intake may increase the CSA of muscle of psoas major.