Acaricidal activities of Momordica cochinchinensis extracts against Tetranychus cinnabarinus were tested in laboratory using slide-dip method.M.cochinchinensis was extracted using methanol,chloroform and petroleum ether respectively.Liquid-liquid partition technique was used to separate the chemical compounds.The acaricidal components were separated by column chromatography and thin layer chromatography.Finally,the principal active component was tested by GC-MS.Cultures of T.cinnabarinus were maintained in the laboratory for three years without exposure to any acaricide.Compared with methanol and chloroform extracts,petroleum ether extracts of M.cochinchinensis showed the highest extraction rate of 30.79%,which is significantly higher than the other solvents extraction rate,and the methanol extraction rate was only 4.58%.The bioassay result showed that the substance extracted using petroleum ether was effective than the others,the corrected mortalities of T.cinnabarinus adult mites was 77.52% after 24 h treatment at the concentration of 2 mg/mL.The Duncan′s test showed that the contact toxicity of the crude extracts from different solvents was significantly different from each other(P0.05).Petroleum ether extract of T.cinnabarinus was found to have high ovicidal activity to T.cinnabarinus and the corrected mortalities of eggs was 72.04%.While very low ovicidal activity was observed with Methanol and chloroform extracts,the corrected mortalities of eggs were 9.85% and 45.56% respectively.The results of liquid-liquid partition showed that acaricidal activity of methanol purification was significantly higher than the part of petroleum ether,the corrected mortalities of adult mites and eggs were 89.60% and 74.65% after 24 h treatment at the concentration of 2 mg/mL,while the part of petroleum ether showed the lower contact toxicity,the corrected mortalities of adult mites and eggs were 70.15% and 25.70%.The oviposition inhibition rate of methanol purification was 62.74% and the repellency rate was 58.23%.Afterwards,the methanol purification of M.cochinchinensis was further purified by silica gel column chromatography,and 10 fractions were got.The acaricidal activity of these 10 fractions to T.cinnabarinus were determined.Fraction 5,6,7 had significantly acaricidal activity.Fraction 5 was found to have the highest acaricidal activity to T.cinnabarinus,the corrected mortality of adult mites was 86.15% after 24 h treatment at the concentration of 2 mg/mL.The median lethal dose was 0.9399 mg/mL and 95% confidence limit was 0.5517—1.6012 mg/mL.The purity and principal component of fraction 5 were detected by TLC and GC-MS respectively.One major constituent was identified by comparison of mass spectral of each peak with those of authentic samples in a Mass Spectra library and confirmed by comparison of retention time obtained by GC with those of authentic compounds.The peak which appeared at about 53.52 min was α-spinasterol with matching of 94%.It was found to have high acarcidal activity to T.cinnabarinus.At the same time the acaricidal activity of α-spinasterol standard was tested.The corrected mortality of adult mites was 92.37% after 24 h treatment at the concentration of 2 mg/mL.So α-spinasterol may be the main acaricidal component of M.cochinchinensis extraction.These data provided useful information for the use of M.cochinchinensis as a novel resource of botanical acaricide.