Objective: Evaluating the effect of vegetable oil, as a supplement to breast milk in increase the weight gaining of VLBW neonates.Materials and methods: In this single blind; Randomized clinical trials, in NICU of Vali-asr Hospital, Tehran University of Medical Sciences, 2005–2006; A total of 48 VLBW neonates referred & admitted to NICU, who did not have any major GI (especially NEC), respiratory or cardiac diseases; participated randomly in two groups: intervention & control. Vegetable oil was added to the milk of 25 neonates (0.5 cc per 30cc of milk) and the other 25neonates with similar conditions that were selected as a control group, did not get any type of supplementary nutrition. Daily feeding volume in both groups was 150-200 cc for each kilogram of body weight.Results: Weight gaining in interventional groups was considerably more than control group. (p<0.04).There were also significant statistical differences in hospitalization period between the two groups, 28.9 days in interventional and 20.33 days in control group, (p<0.03).However, no significant side effects were observed.Conclusions: There is no report regarding contraindication linking the use of vegetable oil intended for appropriate weight gaining or reducing hospitalization period to neonatal chronic diseases.