〔Abstract〕 Objective To evaluate the anti-inflammatory effect of tissue inhibitor of metalloprotease(TIMP1) on a rat model of irreversible pulpitis. Methods An irreversible pulpitis model was established by pulp exposure on maxillary first molars of 8-10 weeks old male rats, and pulpotomy was performed at 24 h, 36 h and 48 h after pulp exposure, with TIMP-1 covering the pulp section(TIMP-1 group) and saline as control(NS group). Coronal obturation were performed with glass-ionomer cement. Histological and immunohistochemical analysis were performed at 24 and 48 h after administration. Results Quantitative histopathological analysis of HE-stained sections showed that the inflammation score(inflammatory cellular response of the root pulp, morphological changes in root pulp tissue and extent of root pulp necrosis) of the pulp were higher in the TIMP-1 group than those in the NS group(P<0.001 orP<0.01). Immunofluorescence staining(CD68-labeled) sections showed that the intensity of CD68 immunofluorescence was higher in the TIMP-1 group than that in the NS group(P<0.001). Conclusion TIMP-1 had no anti-inflammatory effect in a rat model of irreducible pulpitis and increased the degree of inflammation in the root pulp.