Provided is an oil/fat composition comprising 10.1 to 94.9 wt. % of a triglyceride, 0.1 to 30 wt. % of a monoglyceride and 5 to 59.9 wt. % of a diglyceride which has, as a fatty acid constituent thereof, 15 to 90 wt. % of an ω3-unsaturated fatty acid having less than 20 carbon atoms. The oil/fat composition of the present invention has excellent heat stability, has body-fat-accumulation resisting action, visceral-fat-accumulation resisting action, blood-sugar-level lowering action, insulin resistance improving action and leptin lowering action and is useful for, as well as pharmaceuticals, preventive or remedial food for diabetes or obesity, and feed.