Abstract: Hydrolytic rates for technical triazophos and its relevant impurity sulfotep at different pH and temperature were determined qualitatively by gas chromatography-mass spectrometry(GC-MS),and quantified by gas chromatography. The results showed that triazophos belonged to hydrolytically unstable substance. The hydrolysis rates for triazophos at 50℃ after 5 days under pH 5,7,9 were 48.0%,70.7% and 79.4%,respectively. The hydrolysis rates for sulfotep at 50℃ after 5 days under pH 5,7,9 were over 86%. Sulfotep was subject to be hydrolyzed faster than triazophos. Hydrolysis rates for triazophos and sulfotep were significantly affected by temperature. The half-life decrease with temperature. Hydrolysis rates for triazophos increased rapidly with the medium at high pH conditions,while no significant change of hydrolysis rates of sulfotep was observed at alkaline solutions. The hydrolysis rates of triazophos were 1.6~6.0 times slower than that of sulfotep under the same condition. No such difference was observed when pH and temperature was increased.Under the experimental conditions mentioned above,triazophos belongs to the pesticide with a readily to moderately hydrolyzed character,and sulfotep belongs to the pesticide type which could readily be hydrolyzed.