Abstract: To study acaricidal activity of compounds from Gardenia jasminoides Ellis, two hemiterpene were isolated from EtOAc extract of Gardenia jasminoides Ellis by using various chromatographic techniques,and their chemical structure were identified as Geniposide and Ursolic acid on basis of comparing spectroscopic data with literature.Their half lethal concentration(LC50) value against Tetranychus cinnabarinus( Boisduval) were detected as 2.69 mg.ml-1and1.81 mg.ml-1 .And detected that the acaricidal activity of two compounds increased significantly when join with concentration of KOH. The half lethal concentration(LC50) value were detected as 0.94mg.ml-1、0.95 mg.ml-1 .The result showed that Geniposide and Ursolic acid all have significantly higher acaricidal activities,especial when join with KOH.