Objective: To investigate the efficacy and immune tolerance regulation mechanism of partially hydrolyzed whey protein (pHWP) combined with different doses of fructooligosaccharides (FOS) and Bifidobacterium animalis subsp. lactis Bb-12 (Bb-12) in alleviating cow's milk protein allergy (CMPA) in mice. Methods: The four-week-old female BALB/c mice were randomly assigned into normal control， sensitized control， pHWP and pHWP + FOS + Bb-12 intervention groups. During the experimental period (day 0-42)， the mice in the intervention groups were continuously fed with an aqueous solution containing pHWP (15 mg/mL) or pHWP (15 mg/mL)， FOS (0.4 or 4.0 mg/mL) and Bb-12 (1×105 or 106 CFU/mL) instead of drinking water. Mice in the sensitized control group and intervention groups were sensitized by intragastric administration of sterile saline containing 20 mg CMP and 10 μg cholera toxin on day 7， 14， 21， 28 and 35， while mice in normal control group received only sterile saline. On day 42， all mice were oral challenged with 50 mg CMP， and allergic symptom scoring were conducted within 1 h after challenge. Serum antibody and histamine contents， as well as splenocyte proliferation and supernatant Th1， Th2 and Tregrelated cytokine (INF-γ， IL-4 and TGF-β) levels were assessed. Results: The allergic symptom scores (0-1)， serum total IgE (169.4-272.7 ng/mL)， CMP-specific IgE (sIgE) (0.038-0.414 OD)， sIgG1 (0.252-0.379 OD)， and histamine contents (19.56-27.35 ng/mL)， splenocyte proliferation stimulation indexes (1.48-1.58) and supernatant IL-4 levels (18.48-29.60 pg/mL) of mice in the pHWP + FOS + Bb-12 intervention groups were significantly lower than those in the sensitized control group (P<0.05)， while the splenocyte supernatant TGF-β (143.1-177.2 pg/mL)， INF-γ levels (189.5-230.2 pg/mL) and INF-γ/IL-4 ratios (6.46-12.71) were significantly higher than those in the sensitized control group(P<0.05). Compared with pHWP， pHWP + FOS + Bb-12 was more effective in alleviating CMPA， especially when high dose of Bb-12 (1×106 CFU/mL) was applied. No significant difference was found in serum total IgE， CMP-sIgE， splenocyte supernatant IL-4 and INF-γ/IL-4 between pHWP + FOS + high dose Bb-12 intervention groups and normal control group mice. Conclusion: PHWP combined with FOS and Bb-12 could effectively ameliorate CMPA symptoms in mice by improving CMP immune tolerance， which may be related to blocking the secretion of IgE， CMP-sIgE， sIgG1 and histamine， inhibiting the proliferation of splenocytes， and upregulating the level of TGF-β and the ratio of INF-γ/IL-4.