Objective To choose the best retraction agent for the clinic by evaluating cytotoxic effects of six chemical retraction agents on human gingival fibroblasts（HGF） in vitro. Methods HGF were treated with six chemical retraction agents which included 20% Al2（SO4） 3, 5% Al2（SO4） 3, 15.5% Fe2（SO4） 3, 13.3% Fe2（SO4） 3, 0.1% HCl - epinephrine and 0.01% HCl-epinephrine. The damage of direct contact and proliferation inhibit were observed by methyl thiazolyl tetrazolium（MTT） colorimetric assay, the ultra structure was observed under transmission electron microscope（TEM）. Results All of chemical retraction agents caused cell damage and proliferation inhibit. The ability of cytotoxic effect increased in an order of 0.01% HCl-epinephrine
