ACPP, also known as prostatic acid phosphatase isoform PAP, is a type I integral membrane protein of the plasma membrane and lysosomes, and a secreted form also exists. The concentration of ACPP is elevated in the circulation of prostate cancer patients, making the enzyme a marker for the progression of prostate cancer. Recombinant human ACPP, fused to His-tag at C-terminus, was expressed in insect cell and purified by using conventional chromatography techniques.