Background: Previous studies have indicated B cells as potential predictive markers for anti-PD-1 blockade therapy in several cancer types. The study explored whether B cells in TME and B cell related gene signatures are associated with clinical benefit (CB) for ESCC patients receiving anti-PD-1/PD-ligand 1 (PD-L1) therapy. Methods: Sixty-six ESCC patients treated with PD-1/PD-L1 blockade-based immunotherapy were enrolled. Tumor response was evaluated per RECIST 1.1, and CB was defined as complete response, partial response or stable disease at least 6 months. Transcriptome of formalin-fixed paraffin-embedded ESCC tissues were generated by NanoString nCounter platform with Human PanCancer Immune Profiling panel (n=25), Gene Set Enrichment Analysis (GSEA) was performed to identify the differential immune-related pathways, and CIBERSORT was applied to estimate the levels of infiltrating immune cells. The expression of CD20 was evaluated by immunohistochemistry (IHC) (n=66). Results: Of 66 enrolled patients (M: F= 65: 1, median age of 59), 44 and 22 were of recurrent and de novo metastatic ESCC. Forty and 26 received PD-1/PD-L1 blockade alone and PD-1/PD-L1-based combination immunotherapy, respectively. The response rate was 17%, and the CB rate was 24%. The median progression-free-survival (PFS) and overall survival are 1.8 and 5.5 months, respectively. B cell signature was significantly increased in patients with CB (P< 0.05) and associated with longer progression-free survival and overall survival (both P< 0.05). The genes related to B cells, B cell functions, and T cell functions were up-regulated in patients with CB compared to that with non-CB (all P< 0.05). Naïve B cells and plasma cells were significantly increased in patients with CB (both P< 0.05). The expression levels of stromal CD20 by IHC trended to increase in patients with CB (P = 0.08). Conclusions: B cells in tumor microenvironment may be associated with CB of anti-PD-1/PD-L1 therapy in patients with ESCC. (Funded by MOST 105-2314-B-002 -186 -MY3; MOHW107-TDU-B-211-114017; MOST 108-2314-B-002 -076 -MY3; MOST 107-2314-B-002-199 -).