Objectives: The aim of this study was to measure the upper and lower body aerobic capacity of semi-elite Rugby League (RL) players. Methods: Twenty-two semi-elite RL players and 24 physically active but untrained men completed a maximal oxygen consumption test (VO2 max test) on a treadmill and electronic arm ergometer in a randomized order. Percent body fat was calculated from the sum of six skinfolds. Results: Lower and upper body absolute (P=0.03 and P=0.02 respectively) but not relative VO2 max was higher in the RL group compared to the control group. Upper body peak power (P=0.001), ventilation (P=0.05) and lactate concentration (P=0.03) were higher in the RL group compared to the control group. Maximum heart rate was lower during arm ergometry for both groups (P ≤ 0.001) compared to predicted and treadmill values. Conclusions: The results show that while semi-elite RL players have above average lower body aerobic capacity their upper body aerobic capacity is not well developed and similar to untrained men. Coaches and players need to implement separate and dedicated training programs to enhance the development of the upper body aerobic system in RL players. Upper body training should be based on maximal heart rate values achieved during upper body maximal testing.