Chlorinated ethylenes have been recognized for their environmental persistence and risk. Main initial environmental contaminants are tetrachloroethylene and trichloroethylene but dichloroethylenes persist as a by-product of them, because the dechlorination rate of dichloroethylenes is inferior to initial chemicals in general chemical degradation or bioremediation. They protract the absolute remediation of soil and groundwater. This paper describes the dechlorination ability of pyrite, which can degradate the dichloroethylenes at the grater than or equal to the rate of tetra- or tri- chlorothylenes. In our previous research, the chemical reductive ability of natural sulfide for trichloroethylene was clarified and the reaction process differs completely from that with transitional metals. As same as the reaction of trichloroethylene with sulfide, the dichloroethylenes are entirely dechlorinated and change into to non-contaminated hydrocarbone or sulfur compounds. These reaction products adsorb on hydrophobic pyrite surface in this system. The chemical dechlorination is caused by electron sourced from the dissolution of pyrite at normal temperature and pressure condition. The remediation is easy to proceed in the natural environment.