A process is disclosed for the preparation of an optically active or racemic cyclopropanecarboxylic acid of the formula (I) ##STR1## wherein R.sup.1 and R.sup.2 are the same or different and each is lower alkyl or halogen;R is a member of a group which contains various cyclic structures as set forth in the specification,the .about. valency bond represents .alpha.- and/or .beta.-configuration;the -- valency bond represents .beta.-configuration,which comprises reacting an optically active or racemic cyclopropanecarboxylic acid of the formula (VII) ##STR2## with a dimethyl-methylidene-ammonium salt of the formula (VIII) ##STR3## wherein X is halogen or lower alkoxy andY.sup.- is a halide or lower alkylsulfate ion in an anhydrous, inert organic solvent, and sebsequently reacting a dimethyl-acloxy-methylidene-ammonium salt thus obtained with an optically active, inactive or racemic alcohol of the formulaR--OHwithout isolation, in the presence of an organic base.