To investigate the therapeutical effect of the chitosan (CS) nana-paritclessingle administration of Bla g 7 polypeptide - CS nanoparticles used as a BLa g7 polypeptide antigen in the sensitized mice and to explore its immune mechanism, the polypeptide Bla g 7 was enclosed into CS to develop the Bla g 7 polypeptide entrapped CS nano-particles. In the present experiment, 25 BALB/c mice were divided randomly into the Bla g 7 polypeptide treated group(group A , n= 5) , Bla g 7 polypeptide plus CS treated group(group B , n= 5) , CS=control group (group C , n= 5),model group (group D , n= 5) and negative control group (group E, n= 5), After sensitization by intraperitoneal route and challenged by intranasal instillation with crude extracts of German cockroach , the inflammatory changes in the mouse lung tissues were observed after the lung tissues were fixed and stained with haematoxylin and eosin(H&E). The total cell number and the cellular composition of bronchoalveolar lavage fluid (BALF) were detected; and the changes of the mouse airway hyper-reactivity were determined by the whole body plethysmograohy pre-and post-treatments. In these ways, the Bla g7 peptide CS nano-particel vaccine was successfully developed. It was found that the pathological changes in mouse lungs in group D were not so prominent in comparison with those of group A of mice sensitized with crude extract of German cockroach. in which the development of eosinophil infiltration in the airway of mice in D group could be demonstrated. The lung inflammatory reactions and the mucus secretion in lungs of D group were significantly alleviated than those of the B group. but there was no therapeutical effect for the mice fed with the isodoses of Bla g 7 polypeptide or CS. It was also shown that the airway hyper-reactivity of mice was depressed after treatment (P<0.05). It is evident that CS nano-particles show definite therapeutical effect and may serve as a powerful vehicle to improve the tolerance effect of the Bla g 7 polypeptide-CS nanoparticle vaccine, and a single administration of Bla g 7 polypeptide-CS nanoparticle vaccine may hold promise as a new strategy to desensitize the Bla g 7 sensitized disease.