Purpose <p>This study aimed to investigate the impact of a functional training prehabilitation program supported by the Prehab® App on the functional capacity, physical activity level, and symptoms of anxiety and depression in cancer patients undergoing major surgery.</p> Methods <p>This before-and-after experimental study was conducted with 38 patients who had a limited ability to attend a fully supervised prehabilitation program, scheduled for tumour resection at Hospital Clinic-Barcelona. Outcome measures included: Functional capacity assessed by the 30″ sit-to-stand test (30″ STS), Physical activity (PA) measured by the self-reported PA questionnaire: Yale Physical Activity Score (YPAS) and weekly step count via activity trackers; and the psychological status measured by the Hospital Anxiety and Depression Scale (HADS). All the variables were recorded at the beginning of the prehabilitation program (baseline) and the end of the program (before surgery). The statistical analysis was conducted using the paired-samples <i>t</i>-test.</p> Results <p>Most patients underwent upper gastrointestinal surgery, and the prehabilitation program had a mean duration of 6.5&#xa0;weeks. Participants showed notable improvements in functional capacity assessed by 30″ STS, physical activity assessed by YPAS and in the psychological status after the intervention.</p> Conclusion <p>A functional training prehabilitation program supported by the Prehab® App appears to be effective in improving functional capacity, physical activity and psychological status in cancer patients undergoing major surgery.</p>