Purpose: The controlling nutritional status (CONUT) score is a useful biomarker to evaluate undernutrition. However, there have been few reports describing the correlation between postoperative complications and the CONUT score for pancreatic cancer. Therefore, this study aimed to assess the impact of the CONUT score on the postoperative complications of pancreaticoduodenectomy (PD) in patients with pancreatic cancer. Methods: We retrospectively analyzed 206 consecutive patients with pancreatic cancer who underwent PD over a 12-year duration at our institution. The patients were divided into two groups based on preoperative CONUT scores; their clinicopathological characteristics and surgical outcomes were compared. Furthermore, we compared the CONUT score with preoperative clinical factors and several nutritional biomarkers for postoperative complications using univariate and multivariate analyses. Results: Postoperative complications of Clavien–Dindo grade ≥ IIIa and those of Clavien–Dindo grade ≥ IIIb occurred in 29 (14.1%) and 9 (4.4%) patients, respectively. The high CONUT score (≥5) group indicated that patients with an undernutrition status had a higher postoperative complication rate, poorer relapse-free survival, and overall survival rates than the low CONUT score (≤4) group. Among preoperative clinical factors, a high CONUT score was an independent risk factor for severe postoperative complications. Conclusions: The CONUT score may be a useful parameter in the identification of patients undergoing pancreatic surgery who are susceptible to postoperative complications.