Objective To investigate the expression and function of arginase (ARG) in livers of mice infected with Echinococcus granulosus. Methods Eighteen female BALB/c mice were randomly divided into the infection and control group, 9 mice each. Mice in the infection group were each given 2 000 live protoscoleces of E. granulosus by intraperitoneal injection, while the control group was injected with the same volume of saline. Liver leukocytes were isolated 270 days after infection. The expression levels of ARG and nitric oxide synthase (NOS) were examined by Western blotting, and the protein abundance was analyzed with the Image J software. The ARG activity in liver leukocytes, and urea and nitric oxide contents in liver tissues were assessed with the ARG activity detection kit, urea detection kit and nitric oxide (NO) detection kit, respectively. The expression of ARG-1 in various myeloid cells and CD3ζ in T cells in the liver were analyzed by flow cytometry. Data were analyzed using the SPSS 20.0 software. Results Western blotting showed that the gray value of ARG-1 expression in liver leukocytes in the infection group was 1.03 ± 0.01, which was significantly higher than that in the control group (0.12 ± 0.01, P < 0.01); the expression gray value of ARG-2 and inducible nitric oxide synthase(iNOS) in the infection group was 0.54 ± 0.01 and 0.64 ± 0.02, while that of control group was 0.55 ± 0.02 and 0.59 ± 0.02, respectively; no significant differences were found between the groups (P > 0.05). In the infection group, the ARG activity in liver leukocytes, and urea and NO contents in liver tissues was (0.03 ± 0.00) U/ml, (0.66 ± 0.02) mmol/L and (14.63 ± 1.55) μmol/L, respectively, being significantly different from those in the control group [(0.02 ± 0.00) U/L, (0.04 ± 0.01) mmol/L, and (29.22 ± 0.36) μmol/L, respectively] (P < 0.05). Flow cytometry showed that the relative fluorescence density of ARG-1 expression in CD11b⁺CD11c⁺, CD11b⁺F4/80⁺, CD11b⁺Gr-1⁺, CD11b⁺Gr-1⁺Ly-6C-Ly-6G⁺, CD11b⁺Gr-1⁺Ly-6C⁺-Ly-6G^- and CD11b⁺Ly-6G⁺ liver cells in the infection group were 1.41 ± 0.12, 1.21 ± 0.06, 1.52 ± 0.16, 1.30 ± 0.03, 1.58 ± 0.12 and 1.21 ± 0.04, respectively, all items being significantly higher than those in the control group (1.00 ± 0.14, 1.00 ± 0.05, 1.00 ± 0.01, 1.00 ± 0.07, 1.00 ± 0.03 and 1.00 ± 0.02; P < 0.05). The relative mean fluorescence density of CD3ζ in liver CD4⁺ and CD8⁺ T cells in the infection group were 0.82 ± 0.04 and 0.78 ± 0.05, respectively, both significantly lower than those in the control group (1.00 ± 0.05, 1.00 ± 0.07; P < 0.05). Conclusion Higher expression of ARG-1 in liver leukocytes was found in mice infected with E. granulosus, which may antagonize the NOS to some extent; meanwhile, the expression of CD3ζ in the CD4⁺ and the CD8⁺ T cells was down-regulated.