This investigation focused on the conditions influencing the enzymatic synthesis of galactooligosaccharides(GOS).The GOS yield was analyzed by HPLC and used as experimental index.This article had evaluated the influences of the type and concentration of the buffer solution,the initial lactose concentration,the reaction temperature,enzyme dosage,pH and reaction time on the yield of GOS.The results showed that the optimal conditions for the enzymatic synthesis of GOS were as follows: 0.1 mol/L,pH 7.0 Na2HPO4/NaH2PO4 as buffer solution,the initial lactose concentration of 45%(w/v),the reaction temperature of 55℃,enzyme dosage of 20 U/g lactose and reaction time of 12 h.Under these conditions,the maximum GOS yield was achieved 44.5%.