Background: Frailty, featured by the presence of fatigue, weight loss, decrease in grip strength, decline gait speed and reduced activities substantially increase the risk of falls, disability, hospitalizations, and mortality of older people. Nutritional supplementation and resistance exercise may improve muscle function and reverse frailty status. Objective: To evaluate whether whey protein supplements can improve muscle function of frail older people in addition to resistance exercise. Methods: 115 community-dwelling older adults who met the Fried's criteria for frailty from four hospitals’ outpatients clinic in Beijing, China completed the study. It's a case–control study which whey protein was used as daily supplementation for 12 weeks for active group and regular resistance exercise for active group and control group. Handgrip strength, gait speed, chair-stand test, balance score, and SPPB score were compared in both groups during the 12-week follow-up. Results: Overall, 115 subjects were enrolled for study with 66 in active group and 49 in control group. Handgrip strength, gait speed, and chair-stand time were all significantly improved in both groups with significant between-group differences. The active group improved significantly in handgrip strength compared with the control group, which between-group effect (95% confidence interval) for female was 0.107 kg (0.066–0.149), p = 0.008 and for male was 0.89 kg (0.579–1.201), p = 0.007. For chair-stand time, between-group effect (95% confidence interval) was −2.875 s (−3.62 to −2.124), p = 0.004 and for gait speed, between-group effect (95% confidence interval) was 0.109 m/s (0.090 to 0.130), p = 0.003. Conclusions: The 12-week intervention of whey protein oral nutritional supplement revealed significant improvements in muscle function among the frailty elderly besides aiding with resistance exercise. These results warrant further investigations into the role of a multi-modal supplementation approach which could prevent adverse outcomes among frailty elderly at risk for various disabilities.