Abstract: Objective To observe the apoptosis,expression of telomerase activity and telomerase reverse transcriptase (TERT)mRNA in spermatogenic cells after aniso-doses arsenic(As₂O₃)administration in the testes of adult male rats.Methods Forty health male Sprague-Dawle rats were divided randomly into four groups and were administered respectively with 0(control group),0.375,0.75,1.5 mg/kg As₂O₃ water solution by intragastric administration consecutively for 16 weeks.Ternimal dexynucleotidyl tranferase-mdiated dUTP-biotin nick end labeling(TUNEL)was used to measure the apoptosis of spermatogenic cells of rats treated with arsenic.The telomerase activity and TERT mRNA expression in rat testicle spermatogenic cells were tested by method of immunohistochemistry(ICH)and nucleic acid hybridization in situ(ISH).Results The apoptosis index(AI)of middle dose group and high dose group significantly increased compared with that in the control group(P<0.01).The expression of telomerase activity in middle dose group and high dose group decreased significantly compared with that in the control group(P<0.01).The expression of TERT mRNA in middle dose group and high dose group decreased significantly compared with that in the control group(P<0.01).The negative correlation was significant between apoptosis and telomerase activation of spermatogenic cells(r=-0.896,P<0.01).The positive correlation was significant between telomerase activity and TERT mRNA expression of spermatogenic cells(r=0.832,P<0.01).Conclusion One of the mechanisms of male reproduction toxicity of As₂O₃ might be that telomerase activity is inhibited by the down regulation of TERT mRNA expression,which induces the increase of apoptosis of spermatogenic cells and decrese of quantity of sperm cells.