Abstract: Objective To explore the predictive value of esophageal immune prognostic index(EIPI) on the efficacy and prognosis of advanced esophageal squamous cell carcinoma(ESCC) patients undergoing PD-1 inhibitor therapy.Methods The advanced ESCC patients treated with PD-1 inhibitors at Huai'an Second People's Hospital from June 2019 to November 2022 were included, and their baseline data and laboratory results before treatment were retrospectively analyzed. The patients were then divided into two groups based on the derived neutrophil-to-lymphocyte ratio (dNLR) and lactate dehydrogenase (LDH) before treatment:a good EIPI score group and a moderate/poor EIPI score group. Kaplan-Meier and log-rank tests were used to compare the median overall survival (OS) and median progression-free survival (PFS) between the two groups. A Cox proportional hazards regression model was employed to identify independent prognostic factors.Results A total of 98 patients were enrolled, including 47 patients in the good EIPI score group and 51 patients in the moderate/poor EIPI score group. The good EIPI score group exhibited better efficacy than the moderate/poor EIPI score group (55.3% vs. 35.3%, P=0.046). The median progression-free survival (PFS) (6.2 months) and overall survival (OS) (11.0 months) in the moderate/poor EIPI score group were significantly shorter than those in the good EIPI score group (P=0.02, P=0.008). Multivariate Cox regression analysis revealed that EIPI score was an independent risk factor for PFS (HR=2.11, 95% CI:1.21-3.70, P=0.009) and OS (HR=3.44, 95% CI:1.66-7.14, P=0.001) in ESCC patients undergoing PD-1 inhibitor therapy.Conclusions EIPI score can serve as a predictive indicator for the efficacy and prognosis of ESCC patients undergoing PD-1 inhibitor therapy.