Mineralization is a powerful approach for fine inorganic minerals and organic/inorganic complexs with novel structure. The morphology of composites show the mineralized magnetite dispersed in chitosan hydrogel uniformly. The reason for uniform dispersion might be that the chitosan hydrogel restricted the moving ability of iron ions and the iron ions can only move to the nearest crystal nucleus. The magnetite content of magnetite/chitosan composite was approximately 12.6%. The mineralized magnetite have a significant interaction with chitosan which induced the magnetite/chitosan composite has a higher decomposition temperature than chitosan. After decomposition, the magnetite transformed into γ-Fe2O3 and α-Fe2O3, and a significant crystal growth happened.