Epitranscriptomic RNA modifications constitute a critical gene regulatory component that can affect cancer progression. Among these, the RNA N4-acetylcytidine (ac4C) modification, which is mediated by the ac4C writer N-acetyltransferase 10 (NAT10), regulates the stabilization of mRNA. Here, we identified that the ac4C modification is induced upon cisplatin treatment and correlates with chemoresistance in bladder cancer (BCa). Both in vitro and in vivo, NAT10 promoted cisplatin chemoresistance in BCa cells by enhancing DNA damage repair. Mechanistically, NAT10 bound and stabilized AHNAK mRNA by protecting it from exonucleases, and AHNAK-mediated DNA damage repair was required for NAT10-induced cisplatin resistance. Clinically, NAT10 overexpression was associated with chemoresistance, recurrence, and worse clinical outcome in BCa patients. Cisplatin-induced NFκB signaling activation was required for the upregulation of NAT10 expression, and NFκB p65 directly bound to the NAT10 promoter to activate transcription. Moreover, pharmacological inhibition of NAT10 with Remodelin sensitized BCa organoids and mouse xenografts to cisplatin. Overall, the present study uncovered a mechanism of NAT10-mediated mRNA stabilization in BCa, laying the foundation for NAT10 as a therapeutic target to overcome cisplatin resistance in BCa.