This study aims to investigate the specific predictive role of the preoperative Nutritional Risk Index (NRI) in oligometastatic prostate cancer (OM-PC) patients, who have undergone cytoreductive radical prostatectomy (cRP), and explored its prognostic index values. A total 89 OM-PC patients, who were identified between 2013 and 2019, were included in the present study. The Kaplan-Meier method and Cox regression analysis were used to separately assess the prostate specific antigen (PSA) progression-free survival (PFS). Overall accuracy was determined by analyzing the area under the receiver operating characteristic curve (AUC). The analysis of patients in these three different groups indicated that patients with lower NRI values were significantly associated with a higher Gleason score and more neoadjuvant androgen deprivation therapy (P < 0.05). In addition, the Kaplan-Meier curve analysis revealed that OM-PC patients in the preoperative high-risk group had shorter PSA-PFS (P < 0.001). Furthermore, the multivariate analysis further predicted that the high-risk NRI value is a common independent prognostic factor for shorter PSA-PFS (P < 0.001). Moreover, it was also observed that the AUC value of the NRI score was higher than other conventional nutritional indicators. The present study suggests that NRI can potentially be used as a new prognostic indicator for PSA-PFS for patients with OM-PC after cRP.