The present study investigated the methylation of CpG sites in the cyclooxygenase (COX)‑2 promoter via nuclear factor (NF)‑κB transcriptional regulation and elucidated its effect on the COX‑2 transcriptional expression in a ketamine‑induced ulcerative cystitis (KIC) animal model. The results of the present study revealed that ketamine treatment induced NF‑κB p65 translocation to nuclei and activated COX‑2 expression and prostaglandin (PGE)2 production in bladder tissue, whereas COX‑2 inhibitor suppressed the inflammatory effect. Moreover, DNA hypomethylation of the COX‑2 promoter region located from ‑1,522 to ‑829 bp might contribute to transcriptional regulation of COX‑2 expression and induce a pro‑inflammatory response in KIC. Ketamine treatment increased the binding of NF‑κB and permissive histone H3 lysine‑4 (H3K4)m3, but caused a decrease in the repressive histone H3K27m3 and H3K36m3 on the COX‑2 promoter ranging from ‑1,522 to ‑1,331 bp as determined by a chromatin immunoprecipitation assay. Moreover, in the ketamine group, the level of Ten‑Eleven‑Translocation methylcytosine dioxygenase for demethylation as determined by reverse transcription‑quantitative PCR assay was increased in comparison with the control group, but that was not the case for the level of DNA methyltransferases for methylation. The present findings revealed that there was a hypomethylation pattern of the COX‑2 promoter in association with the level of COX‑2 transcription in KIC.