This study investigated the factors influencing the physical activity (PA) of surgical patients with gastrointestinal cancer. [Participants and Methods] The participants were 28 patients scheduled for elective gastrointestinal cancer surgery (22 men and six women, aged 70.5 ± 8.7 years). Physical functions measured at baseline (before surgery) included body composition, isometric knee extension force, grip strength, 6-minute walking distance, respiratory function evaluation, and one-leg standing time. Baseline laboratory data, including serum albumin (Alb), C-reactive protein (CRP), and total protein levels were also collected. [Results] PA significantly decreased after surgery compared to baseline. Postoperative PA significantly correlated with the Alb level, CRP level, and body fat percentage. [Conclusion] Improvement in PA after surgery in patients with gastrointestinal cancer may be associated with the nutrition status, immune response, and body composition before surgery. Comprehensive interventions before surgery may prevent decreased PA after surgery in patients with gastrointestinal cancer.