Disclosed is a method for production of a fusion protein in which an antibody and a lysosomal enzyme are fused. The method comprises； (a) a step of culturing mammalian cells producing the fusion protein in a serum-free medium to let the mammalian cells secrete the fusion protein in the culture medium, (b) a step of collecting culture supernatant by removing the mammalian cells from the culture medium, and (c) a step of purifying the fusion protein from the culture supernatant by using a column chromatography employing as a solid phase a material to which a substance having affinity for the fusion protein has been bound, a column chromatography employing as a solid phase a material having affinity for the phosphate group, and a size exclusion column chromatography.
