The present invention relates a processing method for nano-miniaturizing chitosan of modifying property, which degrades the chitosan of high molecular weight down to the chitosan of middle and low molecular weight, then primarily nano-miniaturizes the interim chitosan by quaternary ammonium salt/synthesis, finally yield the nano-miniaturized chitosan of modified property by sol-gel method to have features in good biocompatibility and bioactivity to be served as additive material in products of cosmetics, medical treatment, hygiene, health care, biomedicine, agriculture, textile, food and so like so that not only the antiseptic, moisture-retentive and deodorizing capabilities can be promoted but also the processing cost can be reduced due to easiness of the mass production.