Abstract: A herbicidal alkanoic acid derivative of the formula: ##STR1## wherein R is ##STR2## wherein R.sup.3 is a hydrogen atom, a halogen atom, a halogen-substituted alkyl group, an alkyl group, a cycloalkyl group, an alkylthioalkyl group, a hydroxyalkyl group, a hydroxyl group, a cyano group, an acyloxyalkyl group, a thienyl group, a naphthyl group, a dihydronaphthyl group or ##STR3## wherein R.sup.8 is a hydrogen atom, a halogen atom, a nitro group, an alkyl group, an alkoxy group or --S(O).sub.n R.sup.9 wherein R.sup.9 is an alkyl group, and n is an integer of from 0 to 2, m is an integer of from 0 to 2, each of R.sup.2 and R.sup.4 which may be the same or different is a hydrogen atom or an alkyl group, or R.sup.2 and R.sup.4 form together with the adjacent carbon atom a 3-, 4-, 5- or 6-membered ring which may contain an oxygen atom and may be substituted by one or two alkyl groups, each of R.sup.5 and R.sup.6 which may be the same or different is a hydrogen atom or an alkyl group, R.sup.