Disclosed are a dicarboxylic acid compound represented by the formula (I): ##STR1## wherein R represents hydrogen atom, a lower alkyl group, phenyl group or hydroxyl group; R.sup.1 represents a straight or branched alkyl group having 1 to 10 carbon atoms or a lower alkyl group substituted by a group selected from aryl group, a sulfur- or nitrogen-containing heterocyclic monocyclic group and a cycloalkyl group having 4 to 8 carbon atoms; R.sup.2 represents a substituted or unsubstituted aryl group, a cycloalkyl group having 4 to 8 carbon atoms or a sulfur-containing or nitrogen-containing heterocylcic group; X represents sulfur atom, oxygen atom or a substituted or unsubstituted imino group; Y.sup.1 represents imino group, oxygen atom or sulfur atom and Y.sup.2 represents nitrogen atom, or Y.sup.1 represents a vinylene group and Y.sup.2 represents a group: --CH.dbd.; m represents 0 to 3; and n represents 0 or 1, an ester thereof or pharmaceutically acceptable salts thereof, and a process for preparing the same.