Objective: To fully investigate the effect of S100 proteins on the chemoresistance of nonmuscle invasive bladder cancer (NMIBC). Materials and methods: The mitomycin C-resistant bladder cancer cell line M-RT4 was established and liquid chromatography-tandem mass spectrometry was performed for proteomics analysis. RT-PCR and Western blot were then performed to confirm the findings. To investigate the mechanisms, S100A16 was knocked down by siRNA. Then, the sensitivity of M-RT4 to mitomycin C was analyzed by a cell counting kit-8 (CCK8) assay, and the molecular expression including epithelial-mesenchymal transition (EMT)-related and apoptosis-related markers were also examined by Western blot. Based on the cancer genome atlas (TCGA) data, the prognostic value of S100A16 was also investigated. Results: There were six S100 proteins with differential expression, among which S100A16 was confirmed to be the only upregulated protein in M-RT4 cells. The expression of S100A16 was regulated by the EMT-related transcription factor Snail. Knockdown of S100A16 suppressed the AKT/Bcl-2 pathway to promote apoptosis, greatly sensitizing M-RT4 cells to mitomycin C. The expression of S100A16 was negatively correlated with the overall survival of bladder cancer patients. Conclusion: S100A16 contributes to the chemoresistance of NMIBC by promoting the AKT/Bcl-2-mediated anti-apoptosis effect and could be a potential prognostic marker and therapeutic target for NMIBC patients.