Loss of lean body mass is a common problem in many post-treatment cancer patients and may negatively affect physical capacity in terms of maximal muscle strength and functional performance. The purpose of this study was to systematically review the scientific evidence on the effect of progressive resistance training on lean body mass in post-treatment cancer patients. A comprehensive literature search was conducted and ultimately 12 studies were included. Methodological quality of the included studies was evaluated using the PEDro scale and the effect of progressive resistance training was reported as the range of mean changes among RCTs and non-RCTs. Six RCTs and six non-RCTs were included in the study. In the RCTs the change in lean body mass in the progressive resistance training groups relative to control groups ranged from -0.4% to 3.9%, and in four of six trials the training effect was significantly larger than the change in the control groups. In the six non-RCTs, the mean change in lean body mass over time ranged from -0.01 to 11.8% which was significant in two of the trials. The included studies reported no or very limited adverse events following progressive resistance training. Based on 12 heterogenic studies there is moderate evidence supporting a positive effect of progressive resistance training on lean body mass in post-treatment cancer patients.