Alkaline Phosphatase is a group of isoenzymes produced by liver, bones, kidneys, small intestine and placenta. It appears in maternal serum between the 15th and the 26th weeks and increases during the third trimester. Usually, ALP production in maternal serum is not major and total serum ALP level remains normal. Marked elevation of serum ALP may be caused by liver or bone pathology such as malignancy, extra hepatic biliary obstruction, and intrahepatic cholestasis. We report 2 cases of markedly elevated placental isoenzymes of ALP in the third trimester in otherwise uncomplicated pregnancies. In both cases, we have excluded liver, bone, kidney, thyroid, parathyroid, other immunological diseases, and other obstetrics complications. The serum ALP returned to normal level after delivery. We conclude that when markedly raised serum ALP concentration is present during pregnancy, differential diagnosis of other pathology must be excluded. Close monitoring of fetal and maternal conditions, histopathological examination of the placenta, and follow-up of declining ALP concentrations postnatally must be performed. As this condition may have high risk of recurrence in subsequent pregnancies, women should be managed in consultant led clinic.