The purpose of the present study was to compare the effects of different doses of ultraviolet radiation A1 (UVA1) on human fibroblast proliferation and collagen level in a mouse model of scleroderma,so as to identify appropriate irradiation doses for clinical treatment of scleroderma.Monolayer from human fibroblasts was cultured in vitro,and a mouse model of scleroderma was established by subcutaneous injection of 100 μL of 400 μg/mL bleomycin into the back of BALB/c mice for 4 weeks.The mouse models and human fibroblasts were divided into UVA1exposed (100,60 and 20 J/cm 2) and UVA-unexposed groups.At 0,24 and 48 h after exposure,cell proliferation and levels of hydroxyproline and collagen were detected.UVA1 irradiation was performed 3 times weekly for 10 weeks,and the pathological changes of skin tissues,skin thickness and collagen level were observed after phototherapy.Cell proliferation and the levels of hydroxyproline and collagen were inhibited after phototherapy,and there was a significant difference between the UVA1-exposed cells and UVA1-unexposed cells (P < 0.001).In addition,UVA1 phototherapy improved dermal sclerosis and softened the skin,and there were significant differences between the high-dose UVA1 group and the model group,and the negative group (P < 0.05).It is concluded that UVA1 radiation can reduce cell proliferation,and decrease hydroxyproline and collagen levels in a dose-dependent manner in vitro.High-dose UVA1 phototherapy has marked therapeutic effect on scleroderma in the mouse model.Decreased collagen level may be related to the reduced number and activity of cells,as well as inhibition of collagen synthesis. The purpose of the present study was to compare the effects of different doses of ultraviolet radiation A1 (UVA1) on human fibroblast proliferation and collagen level in a mouse model of scleroderma, so as to identify appropriate irradiation doses for clinical treatment of scleroderma. Monolayer from human fibroblasts was cultured in vitro, and a mouse model of scleroderma was established by subcutaneous injection of 100 μL of 400 μg / mL bleomycin into the back of BALB / c mice for 4 weeks. The mouse models and human fibroblasts were divided into UVA1exposed ( 100, 60 and 20 J / cm 2) and UVA-unexposed groups. At 0, 24 and 48 h after exposure, cell proliferation and levels of hydroxyproline and collagen were detected.UVA1 irradiation was performed 3 times weekly for 10 weeks, and the pathological changes of skin tissues, skin thickness and collagen level were observed after phototherapy. Cell proliferation and the levels of hydroxyproline and collagen were inhibited after phototherapy, and there was a significant difference between the UVA1 -exposed cells and UVA1-unexposed cells (P <0.001) .In addition, UVA1 phototherapy improved dermal sclerosis and softened the skin, and there were significant differences between the high-dose UVA1 group and the model group, and the negative group (P <0.05) .It is said that UVA1 radiation can reduce cell proliferation, and decrease hydroxyproline and collagen levels in a dose-dependent manner in vitro. High-dose UVA1 phototherapy has marked therapeutic effect on scleroderma in the mouse model .Decreased collagen level may be related to the reduced number and activity of cells, as well as inhibition of collagen synthesis.