Chitinase producing microorganism was obtained from soil rich in chitin, and its metabolite was separated and purified by the method of salting out and chromatography respectively. Capillary electrophoresis was used to determine the homogenization of chitinase. The result showed that chitinase is homogenous to a certain extent, and its corresponding concentration is about 1.7145mg/ml. The method of double diffusion was employed to study the fractal of magnesium ammonium phosphate crystals (MAPs), and different concentration of chitinase solutions were added into reactive system of MAPs formation in order to investigate effect of chitinase on MAPs fractal. The results indicated that with the increasing of chitinase concentration, initial time of MAPs formation becomes longer and longer, crystal shape smaller and smaller, crystal mass less and less. It is suggested that chitinase could inhibit MAPs formation. MAP was characterized by XRD. The crystal is mainly magnesium ammonium phosphate hexahydrate (MgNH₄PO₄.6H₂O) and a little magnesium ammonium phosphate hydrate (MgNH₄PO₄. H₂O).