Abstract: Objective To investigate the adverse effect of dibutyl phthalate (DBP) on testis of rat and to explore the relationship between extracellular regulated protein kinase (ERK) signaling pathway and gap junction injury.Methods Four groups of Sprague-Dawley (SD) rats were administered with 50,500 or 1000 mg/kg DBP or corn oil (control group) by gavage once a day continuously for 5 weeks.Follicle-stimulating hormone (FSH),luteinizing hormone (LH) and testosterone (T) in serum were detected with enzyme-linked immunosorbent assay (ELISA).The density,mobility and overall malformation rate of sperm in epididymis were evaluated with sperm morphology analyzer.The histopathological changes in testes of the rats of each group were observed with haematoxylin and eosin (HE) staining.Western blot was applied to quantify the expression of extracellular signal-regulated kinases 1 and 2 (ERK1/2) and phosphorylated extracellular signal-regulated kinase 1 and 2 (p-ERK1/2) protein which are responsible for ERK signaling pathway.The mRNA expression of connexin 43 (Cx43),the predominant protein of gap junction,was estimated by reverse transcriptase PCR (RT-PCR).Results The serum testosterone level (6.65±0.97 and 3.57±0.54 nmol/L) of the rats exposed to moderate and high dosage DBP decreased significantly compared to that of the control (both P<0.05);the sperm density (64.71±11.36×10 000/mL) of the rats of high dose DBP exposure group decreased significantly (P<0.05),while the overall malformation rate of sperm (13.64±1.68% and 19.54±2.86%) for the rats exposed to moderate and high dosage DBP increased significantly (both P<0.05).The damage severity of testis tissues of the rats was positively related to DBP exposure dose.The expression of p-ERK1/2 protein in testis tissues for the rats with moderate and high dose DBP exposure increased significantly (both P<0.05) but the expression of Cx43 mRNA decreased for the rats exposed to various doses of DBP significantly compared to those of the control rats (P<0.05).Conclusion DBP could activate ERK signaling pathway and down-regulate Cx43 expression,resulting in structure and function damage in testis tissue in rats.