Postoperative hypoalbuminemia is associated with adverse outcomes, particularly in cancer patients. The risk and predictors of hypoalbuminemia in cancer patients following extensive abdominal surgery (EAS), despite total parenteral nutrition (TPN) support, were evaluated. A prospective cohort study (n = 115) was conducted in patients with gastrointestinal and/or urogenital malignancies following extensive (n = 81) or moderate (n = 34) abdominal surgery (mean age ± standard deviation: 66.0 ± 11.7 years). EAS patients received daily TPN, including 200 mL of 5% human albumin solution. Serum albumin (SA) levels and hypoalbuminemia (SA < 3.5 g/dL) were assessed daily. EAS patients had an elevated risk of hypoalbuminemia during the first postoperative week [relative risk (RR): 3.12; 95% confidence interval (95% CI): 1.64-5.91]. Postoperative hypoalbuminemia was associated with surgery duration (RR: 1.76; 95% CI: 1.32-2.36), preoperative SA (RR: 0.24; 95% CI: 0.11-0.55), blood (RR: 1.46; 95% CI: 1.04-2.04) and Ringer's lactated solution (RR: 1.52; 95% CI: 1.12-2.07) volumes transfused intra-operatively. Therefore, despite TPN, cancer patients who underwent EAS had an elevated risk of postoperative hypoalbuminemia. Additional tailored nutritional support among this group is necessary to deter adverse clinical outcomes.