In　this　paper,　an　impulsive　Lotka-Volterra　competitive　system　with　the　effect　of　toxic　substances　is　considered.　By　using　some　analytical　technique,　we　prove　that　under　certain　conditions　the　species　x(2)　of　the　system　will　be　driven　to　extinction　while　the　species　x(1)　will　be　globally　attractive　with　any　positive　solution　of　an　impulsive　Logistic　equation.　As　a　result,　we　extend　the　principle　of　competitive　exclusion　to　a　T-periodic　competitive　system　with　impulse　and　toxic　substances.　The　main　result　in　this　paper　is　a　good　extension　and　supplement　that　of　Li　and　Chen　(2006).　Furthermore,　the　obtained　results　supplement　the　results　of　Liu　et　al.　(2009).　(C)　2015　Elsevier　Inc.　All　rights　reserved.