Biphenyl derivatives represented by the following formula (1): ##STR00001## wherein R.sup.1 represents a C.sub.5-7 alkyl group, R.sup.2 represents a substituted or unsubstituted aromatic hydrocarbon, or cycloalkyl group, R.sup.3 represents a tetrazolyl group, --NHCOCF.sub.3, --NHSO.sub.2CF.sub.3 or --SO.sub.2NHCONHR.sup.4 in which R.sup.4 represents a substituted or unsubstituted aromatic hydrocarbon group, and Z represents a single bond, a C.sub.1-4 alkylene group or --SO.sub.2NH--, and salts thereof; and ACAT inhibitors and medicines containing them as active ingredients.The compounds according to the present invention possess excellent ACAT inhibitory activities, and are useful as preventives and/or therapeutics for diseases cased by the enhancement of ACAT activity, for example, hypercholesterolemia, atherosclerosis and the like.