It had been found that isofarnesenic acid, synthesized from citronellal, showed a remarkably growth inhibitory action against culture test of avian type tubercle bacilli and also showed a strong antagonism against benzoic acid of oxydase system oxidating benzoic acid, so that dehydrofarnesenic acid, possessing one double bond more than the above compound and ionylideneacetic acid, closely related to vitamin A, were synthesized and their growth inhibitory actions against avian type tubercle bacilli were tested. Both these compounds possessed far weaker action than that of isofarnesenic acid.