Abstract: Novel phenoxyacetic acid derivative of the formula: ##STR1## wherein R is a substituted or unsubstituted phenyl group, naphthyl group or a sulfur-containing 5-membered hetero-monocyclic group, R.sup.1, R.sup.2, R.sup.3 and R.sup.4 are hydrogen atom, a lower alkyl group, a phenyl-lower alkyl group or phenyl group, R.sup.5 is hydrogen atom or a lower alkyl group, R.sup.6 is carboxyl group, a protected carboxyl group, hydroxy group or a di(lower alkyl)-amino group, Ring A is a substituted or unsubstituted phenylene group, m is 0 or 1 and n is an integer 0 to 5, provided that, when m is 0,(1) at least either one of R.sup.1 to R.sup.4 is or/are a phenyl-lower alkyl group or phenyl group,(2) at least either one of R.sup.1 to R.sup.4 is or/are a lower alkyl group, and R.sup.6 is hydroxy group, or(3) all of R.sup.1 to R.sup.4 are hydrogen atom, and Ring A is a substituted phenylene group,or a pharmaceutically acceptable salt thereof are disclosed.

Abstract: Novel phenoxyacetic acid of the formula: ##STR1## wherein Ring A is phenylene group or a phenylene group having 1 to 2 substituent(s) selected from a lower alkyl group, a lower alkoxy group and a halogen atom; either one or two group(s) of R.sup.1, R.sup.2, R.sup.3 and R.sup.4 are a lower alkyl group, and the other groups are hydrogen atom; R.sup.5 is phenyl group or a phenyl group having 1 to 3 substituent(s) selected from a lower alkyl group, a halogen atom a lower alkoxy group and nitro group; and --COOR.sup.6 is carboxyl group or a protected carboxyl group, or a salt thereof are disclosed. Said derivative (I) and a salt thereof have a potent platelet aggregration-inhibiting activity.