Objective To investigate the effect of allergen-specific immunotherapy of recombinant protein Blo t 21 T on asthma in mice sensitized by the extracts of mite Blomia tropicalis. Methods Thirty mice were randomly divided into three groups: the asthma group, the immunotherapy group, and the control group (PBS group)(n = 10 in each group). Mice in the asthma and immunotherapy group were sensitized by intraperitoneal injection of 10 μg B. tropicalis crude extracts formulated with 2 mg Al(OH)₃ in total volume of 200 μl on day 0, 7 and 14. On the 21^th day, the mice were challenged with the same allergen extracts (0.5 μg/ml) through spray inhalation for 30 min for consecutive 7 days. In the immunotherapy group, mice were treated intraperitoneally with 10 μg recombinant Blo t 21 T protein 30 min before the challenge inhalation from 25^th to 27^th days. In the asthma group, mice were not treated. In the control group, mice were not sensitized and treated, only receiving PBS. All mice were sacrificed 24 h after the last inhalation, the sera, bronchoalveolar lavage fluid (BALF) and the lung tissue were collected. The number of eosinophils (EOS) was counted in BALF, the levels of cytokine IL-4, IL-13, IL-17 and IFN-γ in BALF, IgE and IgG_2a in sera were determined by ELISA. The lung histochemical sections were made to evaluate the pathological changes. Single factor F test was used for multiple group comparison. SNK test was used to compare the data from two groups. Results The count of EOS in immunotherapy group was (1.23 ± 0.35) × 10⁵/ml, which was significantly lower than that in asthma group [(5.32 ± 1.22) × 10⁵/ml] (P < 0.05). The levels of IFN-γ, IL-4, IL-13, IL-17 in the immunotherapy group [(316.80 ± 29.12), (70.96 ± 17.62), (159.20 ± 21.08) and (220.80 ± 25.95) pg/ml, respectively] was significantly lower than that in the asthma group [(72.84 ± 10.10), (111.96 ± 13.62), (321.40 ± 31.88) and (425.40 ± 34.83) pg/ml, respectively] (P < 0.05). The levels of IFN-γ, IL-4, IL-13 and IL-17 in asthma group was significantly different from the levels in control group [(125.60 ± 22.38), (12.57 ± 3.62), (109.62 ± 15.38) and (114.38 ± 18.43) pg/ml] (P < 0.05). The level of serological IgG_2a and IgE in the immunotherapy group [(49.73 ± 10.95) and (316.80 ± 29.12) μg/ml, respectively] was higher than that in the asthma group [(27.30 ± 4.83) and (57.40 ± 15.96) μg/ml, respectively] (P < 0.05), however, the levels of IgE in asthma group is higher than that in control group(P < 0.05). HE staining of lung tissue showed that lung tissue in immunotherapy group had reduced pathological changes characterized by the reduced thickened tracheal wall and less inflammatory cell infiltration around the vascular mucosa and lung tissue compared with the un-treated asthma group. Conclusion the Blomia tropicalis recombinant protein Blo t 21 T has allergen-specific immunotherapeutic effect on mite-induced asthma in a mice model.