Background: KDR (kinase insert domain receptor) is the most important VEGF (vascular endothelial growth factor) receptor that mediates the signaling transduction initiated by the VEGF ligands. VEGF signaling can activate angiogenesis which plays a crucial role in tumor growth, metastasis, and treatment response. Here we explore the relationship between KDR mutation and its efficacy of immune checkpoint inhibitors (ICIs) in patients with bladder cancer. Methods: To explore the association between KDR mutations and the efficacy of ICIs in bladder cancer patients, we collected clinical and mutation data of 215 patients who received ICIs (PD-(L)1 and/or CTLA-4 inhibitors) from MSKCC cohort. Gene expression data and WES mutation data of 413 samples in the TCGA database were obtained from the UCSC Xena for analysis of the differences of potential biological mechanisms between KDR-mutant and KDR-wildtype tumors. TMB was calculated as the total number of somatic non-synonymous mutations per megabase. CIBERSORT was applied to infer 22 immune cell type proportions in TCGA advanced bladder cancers. Results: In MSKCC cohort, we observed 5.6% (12/215) samples had KDR mutation. Survival analysis showed that KDR-mutant patients had longer overall survival (OS) than that of wildtype patients (hazard ratio (HR) = 0.27, 95% CI: 0.07-1.09, logrank test P = 0.048); median OS (not reached versus 15 months). Then we compared the TMB between KDR-mutant and KDR-wildtype tumors, the results showed that KDR-mutant group had higher TMB in MSKCC cohort (median [IQR]: 17.58 [11.64–47.81] versus 7.90 [4.92–14.76], P=0.002) and TCGA cohort (median [IQR]: 10.69 [5.87–19.85] versus 4.60 [2.52–8.08], P=0.001). Analysis of 22 immune cell subsets in the TCGA advanced bladder cancers, B cells naive, plasma cells and macrophages M1 were significantly abundant in KDR-mutant tumors (all P <0.05). Conclusions: In ICI-treated bladder cancers, KDR mutation is associated with prolonged OS, higher TMB and activated antitumor immunity, which suggests that KDR mutation may serve as a potential biomarker to guide ICI therapy in bladder cancer.