The invention provides novel substituted phenylpropionic acid derivatives that bind to the receptor as ligands of human peroxisome proliferator-activated receptor (PPAR) to activate and exhibit potent lipid-decreasing action, and processes for preparing them. It relates to substituted phenylpropionic acid derivatives represented by a general formula (1) ##STR1##

[wherein R¹ denotes a lower alkyl group with carbon atoms of 1 to 4, lower alkoxy group with carbon atoms of 1 to 3, trifluoromethyl group, trifluoromethoxy group, phenyl group which is unsubstituted or may have substituents, phenoxy group which is unsubstituted or may have substituents or benzyloxy group which is unsubstituted or may have substituents, R² denotes a hydrogen atom, lower alkyl group with carbon atoms of 1 to 4 or lower alkoxy group with carbon atoms of 1 to 3, R³ denotes a lower alkoxy group with carbon atoms of 1 to 3, and the binding mode of A portion denotes —CH₂CONH—, —NHCOCH₂—, —CH₂CH₂CO—, —CH₂CH₂CH₂—, —CH₂CH₂O—, —CONHCH₂—, —CH2NHCH₂—, —COCH₂O—, —OCH₂CO—, —COCH₂NH— or —CHCH₂CO—], their pharmaceutically acceptable salts and their hydrates, and processes for preparing them.