Insecticidal toxicities of the isolated constituent of Eucalyptus dives oil and its analogues were bioassayed. 3-Carvomenthenone was isolated by chromatographic techniques and determined by EI-MS, 13C-NMR,1H-NMR, 1H-1H COSY, and HMQC. In the fumigant bioassay against P. interpunctella, cyclohexenone exhibited the strongest insecticidal toxicity (LD50 against larvae and adults, 2.45 and 3.63 μg/cm3), followed by methylcyclohexenone, seudenone, and 3-carvomenthenone. In the structure-activity relationships between 3-carvomenthenone analogues and insecticidal toxicity, the mode of the insecticidal action of 3-carvomenthenone, cyclohexenone, methylcyclohexenone, and seudenone was through the dermal organs of T. castaneum and P. interpunctella. This study indicates that 3-carvomenthenone, cyclohexenone, methylcyclohexenone, and seudenone have potential capacity for the development as safety natural agents to control the stored grain insects.