Abstract: Nonionic surfactant of special phenylethyl phenol formaldehyde resin polyoxyethylene ether and anion surfactant of calcium dodecylbenzene sulfonate were used as mixed surfactants with mass ratio at 3 to 7,with chlorpyrifos xylene solusion at 75% mass percentage as oil phase,to form chlorpyrifos microemulsion.The transparent temperature region of the microemulsion was determained by turbidness phenomena when temerpature was slowly raised or desreased.Effects of electrolytes and pH on the transparent temperature region of chlorpyrifos microemulsion were investigated.The results show that the addition of electrolyte and the surfactant content could influence on the transparent temperature region of chlorpyrifos microemulsion.The upper limit of transparent temperature of the systems gradually decreased with the increasing of cationic content,but the change of the lower limit of transparent temperature was relatively small.The upper limit of transparent temperature increased firstly with the increasing of anionic content,and then decreased.In both strong acid and strong base solutions,the upper limit of transparent temperature decreased,with a maximum value achieved at weak acid medium.The lower limit of transparent temperature region increased slightly with the increase of pH value.