The methanolic extract from a Chinese endemic Chrysanthemum plant, Dendranthema indicum var. aromaticum, was found to show high antifeeding activity against Pieris brassicae L., and by bioassay-guided separation, the ac-tive component, B-ring-homo-tonghaosu, 2-(2’,4’-hexadiynylidene)-1,6-dioxaspiro-[4,5]-dec-3-ene (2) was isolated. Its structure was elucidated by comparing its spectroscopic data with those of 2 reported in the literatures. Further-more new convenient total synthesis methods of B-ring-homo-tonghaosu were also developed to confirm its struc-ture and make its further application in crop protection available. In addition, extensive comparison of spectroscopic data showed that the structure of compound 21 reported in literature should be revised to 2. The methanolic extract from a Chinese endemic Chrysanthemum plant, Dendranthema indicum var. Aromaticum, was found to show high antifeeding activity against Pieris brassicae L., and by bioassay-guided separation, the ac-tive component, B-ring-homo- tonghaosu, 2- (2 ’, 4’-hexadiynylidene) -1,6-dioxaspiro- [4,5] -dec-3-ene (2) was isolated. Its structure was elucidated by comparing its spectroscopic data with those of 2 reported in the literatures. Further-more new more total synthesis methods of B-ring-homo-tonghaosu were also developed to confirm its strucure and make its further application in crop protection available. In addition, extensive comparison of spectroscopic data showed that the structure of compound 21 reported in literature should be revised to 2