Pure (+)-trans-chrysanthemic acid was synthesized from (+)-Δ3-carene. Ozonolysis of (+)-Δ3-carene affords 2, 2-dimethyl-3-(2-oxo-propyl)-cyclopropyl-acetalde-hyde which was cyclized to (-1-)-2-acetyl-6, 6-dimethyl-bicyclo-[3, 1, 0]-2-hexene. The bicyclo compound was transformed into (+)-cis-homocaronic acid by ozonolysis followed by oxid-ation. Diester or anhydride of the acid and methyl magnesium iodide gave (-)-dihydro-chrysanthemolactone which afforded finally (+)-trans-chrysanthemic acid via ethyl (-)-cis-chrysanthemate.