Aim: The aim of this study was to examine the effect of the prognostic nutritional index (PNI) value on survival in patients with rectum cancer who received postoperative chemoradiotherapy.Material and Methods: The study included 65 patients who received adjuvant chemoradiotherapy. Radiotherapy of 5040 cGy and simultaneous 5-FUFA chemotherapy was given to the patients. The patients were divided into 2 groups as PNI ≤46 and PNI >46 according to the ROC analysis. The differences in survival between the groups were calculated with the log-rank test. The univariate and multivariate hazard ratios were calculated using the Cox proportional hazard model.Results: The patients included 22 (33.8%) females and 43 (66.2%) males. The low PNI group comprised 28 (43.1%) patients and the high PNI group, 37 (56.9%). According to the Kaplan-Meier analysis, mean survival was 59 months (95% CI; range, 44.95-73.08 months) in the low PNI group and 80 months (95% CI; range 66.53- 94.82 months) in the high PNI group. The 5-year survival rate was 49% in the low PNI group and 65% in the high PNI group. In the univariate analysis, T stage, N stage, tumor diameter and PNI had an effect on overall survival (p<0.05). In the multivariate Cox regression analysis, T stage (p=0.014), tumor diameter (p=0.023) and PNI (p=0.045) were found to be prognostic factors affecting overall survival independently of the other variables.Discussion: The results of the study showed that the PNI value before radiotherapy is a poor prognostic factor for rectum cancer.