Objective: To investigate the effect of two types of triterpenoids combined with amoxicillin (Amo) on respiratory tract infection in rat pups and its immunol. mechanism. Methods: Six of 42 SD rat pups were selected as the normal group (normal saline), and the other pups were used to construct the respiratory tract infection model by throat opening and dropping Klebsiella suspension. After modeling, the rat pups were randomly divided into model group (normal saline), Amo group (1 mg/kg), ursolic acid (UA, 5 mg/kg) group, Ganoderma acid B (GA-B) group (3 mg/kg GA-B), Amo + UA group (1 mg/kg Amo + 3 mg/kg GA-B), and Amo + GA-B group (1 mg/kg Amo + 3 mg/kg GA-B). All groups were gavaged with corresponding drugs once a day for 7 days. On day 1 (before administration) and day 7 (7 days post administration) of the treatment, the orbital blood of rat pups in each group was taken, and the leukocytes (WBC), red blood cells (RBC), hypersensitive reactive protein (CPR), Hb (HGB), serum T lymphoid (T) cells, and B lymphoid (B) cells were detected by automatic blood analyzer and flow cytometry. The levels of T cells and B cells were detected by polychromatic marker combination (CD3+, CD4+, and CD8+) antibody and apc-cd19 antibody; Serum interleukin-2 (IL-2), IL-6, IL-10, and IL-1 were detected by ELISA (ELISA) β Level. On day 7 after blood collection, the rat pups in each group were anesthetized and decapitated, followed by collecting the lung tissues to study hematoxylin eosin (HE) staining. The alveolar lavage fluid (BALF) was extracted and the fluorescence values of M2 macrophages (CD206) and M1 macrophages (CD86) in BALF were detected by flow cytometry. Results: Compared with the Amo group, the morphol. of bronchial lumen in Amo + GA-B group significantly returned to normal after treatment, in which no inflammatory cell infiltration or congestion was observed Compared with the Amo and GA-B group, Amo + GA-B group could reduce the level of WBC and CRP, and the difference was statistically significant (P<0.05); Compared with the Amo group, Amo + GA-B group had significant differences in serum IL-2, IL-10, and IL-1β, which decreased by 43.7%, 27.1%, and 32.2%, resp. (P<0.05). Compared with the Model group, GA-B group could increase the signal of APC-CD206 and reduce the signal of PE-CD86; UA group could reduce the signal of APC-CD206 and increase the signal of PE-CD86, in which significant difference was observed between the two groups (P<0.05). Compared with the model group, the combined antibodies (CD3+, CD4+ and CD8+) signal in GA-B, UA group, Amo + GA-B group, and Amo + UA group increased, in which significant difference was found among the four groups (P<0.05). There was no significant difference in the level of CD19+ among rat pups in each group after treatment (P>0.05). Conclusion: GA-B combined with Amo can improve the effect of treating respiratory tract infection in rat pups, and its mechanism may be related to the increasing of M2 polarization of macrophages and reducing of M1 polarization of macrophages.