Background: Recent reports show that the preoperative immunonutritional status correlate with the survival rate in cancer patients. The Prognostic Nutritional Index (PNI) and Controlling Nutritional Status (CONUT) score are used as screening tools for immunonutritional status and reported to be a predictor of postoperative recurrence in patients with various gastrointestinal cancers. However, the clinical importance of the PNI and CONUT in breast cancer has not been elucidated. The aim of this study is to investigate the clinical impact of preoperative PNI and CONUT on long-term survival of breast cancer patients. Methods: We retrospectively analyzed 653 consecutive stage I-III breast cancer patients who were treated from January 2002 to December 2013. The PNI score was calculated as 10 x serum albumin (g/dl) + 0.005 x total lymphocyte count (per mm³). The CONUT score is calculated from three parameters, serum albumin, cholesterol, and total lymphocytes count. The patients were divided into two groups according to the PNI and CONUT score. The uni- and multivariate Cox regression analyses were performed to evaluate the prognositic value of the PNI and CONUT in breast cancer. Results: The malnutritional status was observed in 170 (26%) and 131 (20%) patients as low-PNI and high-CONUT, respectively. The relapse-free survival (RFS) and overall survival (OS) rates were significantly lower in the low-PNI group (RFS: p < 0.0001, OS: p < 0.0001) and high-CONUT group (RFS: p = 0.0009, OS: p = 0.0018). In the multivariate analysis, low-PNI was independent prognostic factors for both RFS and OS (RFS: HR2.33, p = 0.032, OS: HR5.01, p = 0.0009). In the subset analysis, the low-PNI group showed poor prognosis especially in the postmenopausal, hormone receptor negative patients. The low-PNI also had poorer prognosis in post-recurrence survival. Conclusions: The preoperative PNI is a strong independent predictor of long-term survival among breast cancer patients.