A present invention provides a process for preparing a mixture of cyclic terpenoids of general formula (I), ##STR1## wherein R is a hydrogen atom or a lower alkyl group, and general formula (II), ##STR2## wherein R is defined as above, containing (I) predominant over (II) by the reaction of an acid with a cyclic terpenoid of general formula (II), or a mixture of cyclic terpenoids of general formulas (I) and (II), containing (II) predominant over (I).