A chitosan membrane containing nanosize particles is disclosed in this invention. The chitosan membrane comprises a chitosan membrane and nano-inorganic particles. The nano-inorganic particles are uniformly embedded in the chitosan membrane. This invention also discloses a method for forming a chitosan membrane containing nanosize particles. The method comprises a grinding process, a dissolution process, a dispersion process, a blending process, an impurity removing process, a degassing process, a casting process, and a fixation process.