Purpose: Sarcopenia, the loss of muscle mass combined with the loss of muscle function, has become a public health issue. There is an urgent need for interventions. The study aimed to determine the effect of high-intensity resistance training (HI-RT), a time-and cost-efficient training modality, on sarcopenia in osteosarcopenic (OS) older men. Methods: Forty-three community-dwelling men aged ≥72 years from Northern Bavaria, Germany, with OS were randomly assigned to either an active HI-RT group (HI-RT) or an inactive control group (CG). Both received dietary protein (up to 1.5 g/kg/day in HI-RT and 1.2 g/kg/day in CG) and Vitamin-D (up to 800 IE/d) supplements. The HI-RT was applied as a consistently supervised single-set training on resistance exercise machines using intensifying strategies, with two training sessions/week, structured into three phases (ranging from 8 to 12 weeks) totaling 28 weeks. The primary study endpoint was the Sarcopenia Z-score; secondary endpoints were changes in the underlying physiological parameters, skeletal muscle mass index (SMI), handgrip-strength and gait velocity. Results: The results show a significant effect of the exercise intervention on the sarcopenia Z-score in the HI-RT (p<0.001) and a significant worsening of it in the CG (p=0.012) in the intention-to-treat analysis, as well as a significant intergroup change (p<0.001). Analysis upon the underlying parameters showed a significant increase of skeletal muscle mass index (SMI) in the HI-RT group (p<0.001) and a significant intergroup difference of SMI (p<0.001) and handgrip strength (p<0.001). There were no adverse effects related to dietary supplementation or training. Conclusion: The results clearly confirm the favorable effects of HI-RT on sarcopenia. We conclude that HI-RT is a feasible, highly efficient and safe training modality for combating sarcopenia, also in the elderly.