Objectives. Obesity-related physiological changes can limit improvements of obese subjects after training. The aim was to investigate obesity, muscular strength, and physical function in community-dwelling nonsarcopenic old adults. Methods. Nonsarcopenic subjects (, 73.7 ± 5.7 years; 21% normal weight, 42% overweight, and 37% obese based on body mass index (BMI)) participated in a 12-week resistance exercise program. Leisure time physical activity (LTPA), body composition (dual-energy X-ray absorptiometry), quadriceps strength (maximum voluntary isometric contraction; absolute and relative to body weight), and physical function in terms of 6-minutes-walk-for-distance (6MWD) and timed up and go (TUG) were measured baseline and endpoint. Results. At baseline, normal weight participants had lower absolute quadriceps strength (−43 ± 22 N, ) than obese, but better quadriceps strength relative to body weight (1.4 ± 0.7 N/kg, ), 6MWD (53 ± 27 m, ), and TUG (−1.4 ± 0.7 sec, ). LTPA was positively associated with 6MWD and TUG (both ), but based on general linear models, differences in LTPA between BMI categories did not explain differences in 6MWD and TUG between BMI categories. During the program, dropout (11.9%) and attendance (85%) were similar between BMI groups. After the intervention, body composition and physical function significantly improved in all three BMI categories; however, normal weight participants lost more body fat (−1.53 ± 0.78%, ), gained more lean mass (0.70 ± 0.36 kg, ) and relative quadriceps strength (0.31 ± 0.16 N/kg, ), and improved more on the 6MWD (24 ± 12 m, ) but gained less grip strength (−2.4 ± 1.3 N/kg, ) compared to obese. There were no differences in TUG or absolute quadriceps strength changes between the BMI strata. Physical function at baseline as well as training success of overweight participants was located between the normal weight and obesity groups. Conclusion. Nonsarcopenic obese community-dwelling old adults have lower physical function than their normal weight counterparts. This difference is not explained by lower LTPA. A 12-week resistance exercise program improves body composition and physical function in normal weight, overweight, and obese old adults; however, obese participants experience less favorable changes in body composition and physical function than normal weight individuals. This trial is registered with NCT01074879.