ACP5, also known as tartrate-resistant acid phosphatase type 5, is involved in osteopontin and bone sialoprotein dephosphorylation. Its expression seems to increase in certain pathological states such as Gaucher and Hodgkin diseases, the hairy cell, the B-cell, and the T-cell leukemias. Recombinant human ACP5, fused to His-tag at C-terminus, was expressed in insect cell and purified by using conventional chromatography techniques.