Objective To investigate the expression of macrophage subtypes in mouse model of unilateral ureter obstruction (UUO) and its role in renal fibrosis. Methods A total of 39 male C57/BL mice were divided into sham group (n=9), UUO-3d group (n=10), UUO-7d group (n=10) and UUO-14d group (n=10). Unilateral ureter separation was performed on the mice in the sham group, and unilateral ureteral ligation in the UUO groups. The kidney was obtained at 3,7 and 14 days after operation. Pathological staining was used to observe renal interstitial fibrosis and infiltration of inflammatory cells, and immunofluorescence to observe renal interstitial macrophage infiltration. Flow cytometry was performed to detect changes in the proportion of renal macrophage subtypes (CD86 and CD206). SPSS statistics 20.0 was used for data analysis, and SNK-q test for comparison. Results In the sham group, the renal tubules were structurally intact, and the renal interstitium was clear without infiltration of the inflammatory cells and collagen deposition and with infiltration of a small number of macrophages. Compared with sham group, all UUO groups (UUO-3d, -7d, -14) had larger collagen protein areas [(7.8±1.5) % vs (14.1±2.7)%, (27.4±3.1)%, (39.3±2.7)%] and more inflammatory cells [(169±16) vs (1068±164), (2159±432), (3536±318)] in renal interstitium (P<0.05). Prolonged obstruction time in the model group resulted in significantly increased infiltration of macrophages [(20.8±2.7)% vs (31.1±1.3)%, (49.5±2.1)%, (69.6±1.8)%; P<0.05]. The expression of M2 macrophage marker (CD206) also increased with prolonged UUO [(3.2±1.9)%, (34.1±2.1)%, (52.6±1.6)%, (76.7±2.3)%; P<0.05], but no significant difference was found between UUO groups in the expression of M1 macrophage marker (CD86) [(76.4±3.6)%, [JP+2](81.8±2.8)%, (80.6±4.4)%, (85.5±2.6)%; P>0.05].Conclusion Increased M2 macrophage may contribute to renal fibrosis in the mice with unilateral ureteral ligation.