To reveal the molecular mechanisms underlying oral ulcerative mucositis-induced pain, we investigated putative pain-associated mediators, pain-related behaviors and gene modulation in a rat oral mucositis model. On day 1 after acetic acid treatment, the mucosal area showed slight redness and swelling but no evidence of ulceration or pain induction. On day 2, oral ulcers were obvious, as was the induction of spontaneous and mechanical pain. In the treated mucosal area, bacterial loading and prostaglandin E2 increased beginning on day 2; no significant changes were observed on day 1. DNA microarray analysis of trigeminal ganglion tissue collected on day 2 identified 32 significantly regulated genes (>1.5-fold change in expression). The up-regulation of the top 3 genes, Hamp (hepcidin antimicrobial peptide), Reg3b (regenerating islet-derived 3β) and Serpina3n (serine peptidase inhibitor A3N), was validated through quantitative RT-PCR. Systemic antibiotic pre-treatment did not increase the mRNA levels. Therefore, we conclude that the oral ulcerative mucositis-induced pain is caused by infectious inflammation of the ulcerative area and stimulates anti-bacterial and anti-peptidase gene expressions in sensory neurons. Oral ulcerative mucositis-induced gene expression in trigeminal ganglion tissue was measured. Ten Wistar rats were divided into the following two groups, control, oral ulcerative mucositis (stomatitis). Five rats were anesthetized with sodium pentobarbital. A piece of filter paper was soaked in 50% acetic acid diluted with water and placed in the labial fornix region of the inferior incisors of rats for 30 sec. Other five rats received only anesthesia without any treatment were used as a control. On day 2 after acetic acid treatment, oral ulcerative mucositis was obvious and trigeminal ganglion tissues in two groups were collected for DNA microarray analysis.