Enhanced recovery after surgery protocols emphasize the importance of early postoperative mobilization. However, literature quantifying actual physical activity after major abdominal cancer surgery is scarce and inconclusive. A single-center prospective cohort study was conducted at the University Medical Center Groningen from 2019 to 2021. Patients’ postoperative physical activity was measured using an accelerometer, with the primary aim of assessing daily physical activity. Secondary aims were identifying patient-related factors associated with low physical activity and studying the consequences of low physical activity in terms of complication rate and length of hospital stay. 143 patients included (48 % male; mean age 65 years), 38.5 %, 24.5 %, 19.6 %, and 14 % underwent pancreatic, hepatic, colorectal, or cytoreductive surgery with hyperthermic intraperitoneal chemotherapy, respectively. Median daily step count was low; from median 71 steps on the first to 918 steps on the seventh postoperative day. An association between physical activity and age (OR 3.597, p = 0.013), preoperative weight loss ≥10 % (OR 4.984, p = 0.004), Eastern Cooperative Oncology Group performance status ≥2 (OR 4.016, p = 0.001), midline laparotomy (OR 2.851, p = 0.025), and operation duration (OR 1.003, p = 0.044) was found. An association was observed between physical activity and the occurrence of complications (OR 3.197, p = 0.039) and prolonged hospital stay (β 4.068, p = 0.013). Postoperative physical activity is low in patients undergoing major abdominal cancer surgery and is linked to postoperative outcomes. Although physical activity should be encouraged in all patients, patient-specific risk factors were identified that can aid early recognition of patients at risk of low physical activity.