Background The serum albumin (Alb) level often decreases early in the postoperative period.However,it is unclear whether a decline in the serum albumin level (△Alb) is a predictor of postoperative complications.We aimed to determine the relationship between the △Alb and complications following surgery for rectal cancer (RC).Methods We retrospectively collected the records of patients aged ≥ 18 years who underwent RC surgery between January 2015 and August 2018.We determined the cut-off value of the △Alb using subject working characteristic curve analysis and analyzed complications above grade Ⅱ according to the Clavien-Dindo classification.Single and multifactor analyses of the risk factors for postoperative complications were performed.Results A total of 430 RC patients were included in this study.The area under the △Alb curve was 0.786,with a critical value of 22％.We selected 20％ as the critical point for grouping patients.The total postoperative complication rate was significantly higher in patients who had a ≥ 20％ serum Alb decline than those had a ＜ 20％ serum Alb decline (＜ 20％ △Alb group);with rates of 51.5％ and 16％,respectively (P ＜ 0.001).A multifactorial logistic regression analysis revealed that the △Alb (odds ratio[OR]=4.95,95％ CI=3.126-7.838 P ＜ 0.001),surgical approach (OR =2.374,95％ CI=1.335-4.224 P =0.003),and blood loss (＞200 ml) (OR =1.684,95％ CI =1.043-2.716 P =0.033) were independent risk factors for postoperative complications follow RC surgery.Conclusions The △Alb predicted the incidence of postoperative complications in patients after RC surgery.This could help identify patients at risk of complications early during the perioperative period,thereby helping to more effectively manage high-risk patients.