 Low birth weight infants are premature infants that born with birth weight less than 1500 g. Because these infants have low birth weight, weight gain can be increased by fortifying breast milk after post-natal 7. day. Breast milk fortifiers might be preferred for very low birth weight or extremely low birth weight infants infants with 1000 g birth weight infants for faster weight gain. It does not increase risk of necrotizing enterocolitis or infection; and it has lower incidences of necrotizing enterocolitis and sepsis comparing to formula. Breast milk is usually fortified with 100 cckgday enteral feeding 1,2,3,4. Even though many centers use olive oil to fortify breast milk for many years; there is no study to evaluate its scientific value. Hence it has been known that olive oil based parenteral nutrition solutions are well-tolerated by premature infants, are immunologically more neutral, does not increase proinflammatory cytokines; olive oil is the only fat consumed in its natural form and has antimicrobial and cytotoxic effects, lowers serum cholesterol concentration by decreasing cholesterol absorption, has protective measures against cardiovascular diseases due to antioxidant effects of ingredients such as mono- and poly-unsaturated fatty acids, phenolic substances, tocopherols and carotenoids; olive oil has antioxidant, cell renewal and anti- carcinogenic features because of containing squalene which is precursor of steroid synthesis and help digestion by increasing digestive juice by major pigments such as chlorophyll, pheophytin and chlorophyll 5. 