<b><i>Background/Aims:</i></b> This study examines the feasibility of a preoperative exercise program to improve the physical fitness of a patient before gastrointestinal surgery. <b><i>Methods:</i></b> An outpatient exercise program was developed to increase preoperative aerobic capacity, peripheral muscle endurance and respiratory muscle function in patients with pancreatic, liver, intestinal, gastric or esophageal cancer. During a consult at the outpatient clinic, patients were invited to participate in the exercise program when their surgery was not scheduled within 2 weeks. <b><i>Results:</i></b> The 115 participants followed on average 5.7 (3.5) training sessions. Adherence to the exercise program was high: 82% of the planned training sessions were attended, and no adverse events occurred. Mixed model analyses showed a significant increase of maximal inspiratory muscle strength (84.1-104.7 cm H₂O; p = 0.00) and inspiratory muscle endurance (35.0-39.5 cm H₂O; p = 0.00). No significant changes were found in aerobic capacity and peripheral muscle strength. <b><i>Conclusion:</i></b> This exercise program in patients awaiting oncological surgery is feasible in terms of participation and adherence. Inspiratory muscle function improved significantly as a result of inspiratory muscle training. The exercise program however failed to result in improved aerobic capacity and peripheral muscle strength, probably due to the limited number of training sessions as a result of the restricted time interval between screening and surgery.