ABSTRACT: Serum alkaline phosphatase (ALP) is an individual from a group of zinc metalloprotein enzymes that works to separate a terminal phosphate group from aorganic phosphate ester. Numerous things may cause increments of ALP activity in serum, themost common being obstructive liver disease and metabolic bone disease. An increase of the liver or especially the bone isoform (bone specific ALP) in serum can give important diagnostic data. Bone specific alkaline phosphatase isoenzyme is raised because of increased osteoblastic activity. The most elevated absolute ALP values have been credited to an expanded bone isoenzymelevel because of Paget disease or rickets/osteomalacia. The compound action, which is restricted in the plasma membrane of osteoblasts prior to extracellular delivery, associates with the degree of the infection on skeletal studies and with boundaries of bone resorption. This isoenzymes is regularly raised in developing youngsters and grown-ups over the age of fifty. Reasons for high bone ALP includes bone development, healing fracture, acromegaly, osteogenic sarcoma, or bone metastases, leukemia, myelofibrosis, and once in a while myeloma; soALP is utilized as a tumor marker.Hyperthyroidism, by its impact upon bone, may likewise raise ALP. This article reviews the characteristics, diagnostics and clinical significance of ALP.