A commercially available vegetable oil containing a high concentration (87 %, w/w) of diacylglycerol (DAG) has been investigated in humans and animals for potential beneficial effects in reducing serum TAG concentrations in fasting and postprandial states. Effects of DAG oil as a sole dietary fat source (25 % metabolisable energy) were evaluated in a feline model of hypertriacylglycerolaemia. Eleven adult (1·5 (sem 0·1) years) male cats deficient of lipoprotein lipase (LPL) catalytic activity from a heritable point mutation of the LPL gene were acclimatised to a semi-purified diet containing TAG oil for 21 d. After assignment into two groups, pair-matched by serum TAG concentrations (range 6·1–31·6 mmol/l), the cats were fed the diet with either TAG or DAG oil for 8 d. The dietary fat source was crossed-over and presented for 8 d more. Non-fasting serum concentrations of TAG, cholesterol and NEFA were measured on days 6–8 and days 14–16. Dietary fat source (DAG v. TAG) did not significantly affect food intake (491 (sem 16) v. 486 (sem 14) kJ/kg0·67), body weight or serum concentrations (mmol/l) of TAG (37·1 (sem 4·5) v. 33·9 (sem 3·4)), cholesterol (4·8 (sem 0·3) v. 4·8 (sem 0·2)) and NEFA (1·4 (sem 0·2) v. 1·4 (sem 0·2)). The results show that for a feeding trial of 8 d, DAG oil was well accepted and tolerated by cats but did not reduce hypertriacylglycerolaemia resulting from a deficiency of LPL catalytic activity.