Di- and tri-substituted [(4-oxo-4H-1-benzopyran-7-yl)oxy]acetic acids, and 4-oxo-3-phenyl-4H-furo[2, 3-h]-[1]benzopyran-8-carboxylic acid were synthesized and tested for natriuretic acid uricosuric activities. Among the compounds tested, 3, 5-disubstituted [(4-oxo-4H-1-benzopyran-7-yl)oxy]acetic acids (6c-f, h, n and x) showed potent natriuretic acid uricosuric activities, whereas 4-oxo-3-phenyl-4H-furo[2, 3-h][1]benzopyran-8-carboxylic acid (6dd) possessed only potent natriuretic activity. The structure-activity relationships are also discussed.