Objective To investigate the changes of inflammatory factors interleukin-2 (IL-2) and interleukin 4(IL-4) in the pathogenesis of mouse mastitis. Methods Twelve lactating female BALB/ C mice were randomly divided intothe control group (group A), high concentration group (group B), medium concentration group (group C) and lowconcentration group (group D). Group A was injected with normal saline. Groups B, C and D were injected with differentconcentrations of Staphylococcus aureus, 1. 2×10⁵ CFU/ mL, 1. 2×10⁴ CFU/ mL and 6. 0×10³ CFU/ mL, respectively. Thepathological changes were observed using H&E staining. The expression of IL-2 and IL-4 mRNA and protein in the mousemammary glands were detected by qRT-PCR, immunohistochemistry and western blot. Results The pathologicalexamination showed that the pathological changes of breast tissue were gradually aggravated with the increase of theconcentration of S. aureus. Immunohistochemistry, qRT-PCR and western blot assays showed that the expression levels ofIL-2 in the groups B, C and D were significantly higher than that in the group A ( P < 0. 05) However, as the concentrationof infectious bacteria increased, the expression level of IL-2 gradually decreased. Compared with the group A, the groupsB, C and D showed significantly increased expression levels of IL-4 ( P < 0. 05), but the expression level increasedgradually with the increase of concentration of infectious bacteria. Conclusions The inflammatory factors IL-2 and IL-4 areinvolved in the development of mastitis caused by S. aureus, which lays a foundation for the pathologic mechanism of S.aureus mastitis and provide a theoretical scientific basis for studying the immune mechanism of breast.