Provided is an oil or fat composition that is highly safe and is effective for the prevention or treatment of diabetes without concern over side effects, even when ingested on a continuous basis. The oil or fat composition for the prevention or treatment of diabetes comprises triacylglycerol as an active ingredient, and this triacylglycerol has one or two medium-chain fatty acid residues per molecule and comprises as the structural fatty acids a C 6-10 medium-chain fatty acid and a C 16-24 long-chain fatty acid.
