Abstract: The factors influencing the activity of lipase Ⅷ from Pseudomonas Species and the effect of lipases on fat separation of UHT milk were determined to investigate the means for controlling the activity of lipase and inhibiting the fat separation in UHT milk. The results show that the pH value has significant influence on lipase activity(P<0.01), low temperature heat treatment at 50, 55, 60℃ for 20 minutes are effective to inactivate the lipase Ⅷ(P<0.01). It is found that the activity of lipase Ⅷ(P<0.01) and the extent of fat separation(P<0.05) during storage of UHT milk are significantly reduced by the low temperature heat treatment. It is suggested that the optimum condition for inhibiting the fat separation of UHT milk is heating at 55℃ for 15 minutes.