Abstract: Objective To explore the effects of endostatin pretreatment on fibrosis of human skin fibroblasts and the mechanisms. Methods Human skin fibroblasts were routinely cultured in vitro, and then the cells of passage 3 to 5 were used in the following experiments. The cells were divided into blank control, endostatin, platelet-derived growth factor-BB (PDGF-BB), endostatin+ PDGF-BB, transforming growth factor-β₁ (TGF-β₁), and endostatin+ TGF-β₁ groups according to the random number table, with 3 wells in each group. Cells in blank control group were cultured with DMEM medium for 24 h. Cells in endostatin group were cultured with DMEM medium containing 5 μg/mL endostatin for 24 h. Cells in PDGF-BB group and TGF-β₁ group were cultured with DMEM medium containing 200 ng/mL PDGF-BB and 10 ng/mL TGF-β₁ for 24 h, respectively. Cells in endostatin+ PDGF-BB group were pretreated with DMEM medium containing 5 μg/mL endostatin for 48 h and then cultured with DMEM medium containing 200 ng/mL PDGF-BB for 24 h. Cells in endostatin+ TGF-β₁ group were pretreated with DMEM medium containing 5 μg/mL endostatin for 48 h and then cultured with DMEM medium containing 10 ng/mL TGF-β₁ for 24 h. The content of type Ⅰ collagen in the cell culture supernatant of three wells in each group was determined by enzyme-linked immunosorbent assay. The protein expression levels of α-smooth muscle actin (α-SMA), PDGF receptor β (PDGFRβ), phosphorylated PDGFRβ (p-PDGFRβ), and phosphorylated extracellular signal-regulated protein kinases 1/2 (p-ERK1/2) of three wells in each group were detected by Western blotting. Data were processed with one-way analysis of variance and SNK test. Results (1) Compared with (5.05±0.29) pg/mL in blank control group, content of type Ⅰ collagen in the cell culture supernatant of endostatin group [(4.72±0.37) pg/mL] was close to it (P>0.05), content of type Ⅰ collagen in the cell culture supernatant of PDGF-BB group and TGF-β₁ group [(8.60±0.57) and (9.20±0.64) pg/mL, respectively] was higher (with P values below 0.05). Content of type Ⅰ collagen in the cell culture supernatant of endostatin+ PDGF-BB group [(5.32±0.17) pg/mL] was lower than that of PDGF-BB group (P<0.05), and content of type Ⅰ collagen in the cell culture supernatant of endostatin+ TGF-β₁ group [(5.41±0.20) pg/mL] was lower than that of TGF-β₁ group (P<0.05). (2) Compared with those in blank control group, protein expression levels of α-SMA, PDGFRβ, p-PDGFRβ, and p-ERK1/2 of cells in endostatin group showed no obvious differences (with P values above 0.05), while those in PDGF-BB and TGF-β₁ group were significantly higher (with P values below 0.01). Protein expression levels of α-SMA, PDGFRβ, p-PDGFRβ, and p-ERK1/2 of cells in endostatin+ PDGF-BB group and endostatin+ TGF-β₁ group were significantly lower than those in PDGF-BB group and TGF-β₁ group, respectively (with P values below 0.05). Conclusions Pretreatment of endostatin can inhibit the fibrosis of human skin fibroblast and its transformation into myofibroblast, which may be related to the down-regulation of protein expression of p-PDGFRβ, PDGFRβ, and p-ERK.