Background <p>Preoperative hypoalbuminemia is a common condition in elderly cancer patients and may adversely affect surgical outcomes. This study aimed to evaluate the association between preoperative serum albumin levels and postoperative complications, length of hospital stay, and mortality in geriatric patients undergoing cancer surgery.</p> Methods <p>This retrospective single-center study included 330 patients aged 65&#xa0;years and older who underwent cancer surgery between 2018 and 2024. Patients were divided into two groups based on preoperative albumin levels: hypoalbuminemia (&lt; 3.5&#xa0;g/dL) and normal (≥ 3.5&#xa0;g/dL). Demographic data, comorbidities, surgical details, and postoperative outcomes were compared between groups.</p> Results <p>Of the patients, 46% had hypoalbuminemia. Patients with low albumin were significantly older and more likely to be functionally dependent. The incidence of postoperative pulmonary complications (PPCs) was higher in the hypoalbuminemia group (28% vs. 9%, <i>p</i> = 0.002). Furthermore, these patients had longer ICU and hospital stays and higher 30-day mortality (11% vs. 5%, <i>p</i> = 0.003). Each 1&#xa0;g/dL decrease in preoperative albumin level was independently associated with a 3.49-fold increase in the odds of PPCs (OR 3.49, 95% CI 1.17–10.44). Advanced age and higher ASA class were also associated with prolonged hospital stay, while lower hemoglobin and current smoking were independent risk factors for PPCs.</p> Conclusion <p>Preoperative hypoalbuminemia is a significant and independent predictor of adverse postoperative outcomes in geriatric cancer patients. Preoperative serum albumin may serve as a valuable marker of physiological reserve and perioperative risk stratification in geriatric cancer patients.</p> Trial registration <p>ClinicalTrials.gov, NCT06998030 (registered on 13 May 2025; retrospectively registered).</p>