The aim of this study is to determine the effect of oral probiotic on prevention of feeding intolerance in neonates under 1500 grams. This study is a double blind randomized clinical trial. sixty neonates with birth weigth of less than 1500 grams who need NICU care will enroll in the study. Neonates will be randomly allocated in two groups: Treatment and control. Neonates with gastrointestinal tract obstruction; congenital heart disease; congenitaL anomalies and death in first 72 hour of life and if mother receiving probiotic supplement and formula fed neonates will be excluded from the study. Neonates with inclusion criteria for study divided by two group of treatment and control by discharging white and yellow cards from closed bag. In treatment group, when feeding volume reaches to 5cc/kg/day, will receive 4 drop/day in neonates with weight of 1000-1500 grams and 2 drop/day in neonates with weight of less than 1000 grams and will add to breast milk and will order Q12hour and will continue until full feeding of neonates(120-160cc/kg/day). Routine treatment of background disease will accomplish in control group. Milk will increase 20-30 cc/kg day in every day. Feeding intolerance and NEC and their severity will be diagnosed according following criteria: stage one (suspected NEC): signs and symptoms consist of apnea, letargy, hematochezia, abdominal distention, temperature instability, gastric retention, without radiographic findings. stage two(documented NEC): signs of stage one plus thrombocytopenia with or without metabolic and respiratory acidosis, DIC, abdominal tenderness and existence of pneumatosis or gas in portal vein. stage three(advanced NEC): signs of stage two plus hypotension, bradycardia, sever apnea, respiratory and metabolic acidosis, DIC, clear abdominal tenderness, neutropenia and pneumoperitonitis. After data collection, abdominal distention, vomiting and gastric retention and time to enteral feeding and duration of hospitalization and death will compare between two groups.