Substituted thenoylacetic acid and esters, and pharmaceutically acceptable salts thereof of the following general formula are useful as hypolipidemic agents: ##STR1## wherein Y is selected from oxygen and divalent sulfur; R is selected from a straight or branched saturated hydrocarbon chain containing from 10 to 20 carbon atoms and a straight or branched unsaturated hydrocarbon chain containing from 10 to 20 carbon atoms and from 1 to 4 double bonds; R.sub.1 is selected from hydrogen and an ester group.