More than 100 5-substituted thiazolidine-2, 4-diones were prepared and their hypoglycemic and hypolipidemic activities were evaluated with genetically obese and diabetic mice, yellow KK. The structure-activity relationship study showed that the 5-(4-oxybenzyl) moiety is essential for substantial activity. Among these compounds, 5-(4-cyclohexylmethoxy) benzylthiazolidine-2, 4-dione (47), 5-[4-(1-methylcyclohexylmethoxy) benzyl]-thiazolidine-2, 4-dione (49, ADD-3878) and 5-{4-[2-(3-pyridyl) ethoxy] benzyl} thiazolidine-2, 4-dione (59) exhibited the most favorable properties in terms of activity and toxicity.