BACKGROUND: Immunotherapy has demonstrated potential in the treatment of esophageal cancer (EC); however, the overall response rate (ORR) remains below 30% among EC patients. Herein, the use of peripheral blood lymphocyte subsets as biomarkers was explored to evaluate the efficacy of immunotherapy in this patient population. METHODS: Sixty-three patients were enrolled. The patients were diagnosed with EC and treated with immune checkpoint inhibitors (ICIs) at The Fourth Hospital of Hebei Medical University from December 2019 to June 2023. Kaplan-Meier (KM) survival curves were used to reflect differences in survival benefit. The prognostic factors of survival were investigated using the Cox proportional hazards regression model for both univariate and multivariate analyses. Two-tailed P values were reported and statistical significance was defined as P < 0.05. RESULTS: The results of univariate and multifactorial Cox regression analysis for progression-free survival (PFS) revealed that only CD8+ T lymphocytes demonstrated a significant association with PFS (P = 0.034, P = 0.020). Additionally, the multifactorial Cox regression analysis results for overall survival (OS) revealed a significant association between natural killer (NK) cells and OS (P=0.049). Further, a systematic analysis was conducted on the CD8+ T cell biomarker. The KM survival curves indicated that the group with low CD8+ T cell levels experienced a significantly greater PFS benefit compared to the high CD8+ T cell group (P = 0.030). CONCLUSION: The present study reveals that the reduction of both CD8+ T lymphocytes and NK cells in peripheral blood lymphocyte subsets after immunotherapy can serve as superior predictors for the effectiveness of ICIs in patients diagnosed with EC.