Objective To compare the changes of skin thickness and collagen content in mouse models of scleroderma after irradiated with different doses of UVA1, so as to seek the suitablc irradiation dose in the treatment for scleroderma. Methods Sixty mice were randomly and equally divided into 6 groups: blank control group (no injection and no irradiation), model control group (injected only and killed 2 days after the last injection), high-dose (HD) UVA1 group (injected with bleomycin and irradiated with UVA1 of 100 J/cm2), medium-dose (MD) UVA1 group (injected with bleomycin and irradiated with UVA1 of 60 J/cm2), low-dose (LD) UVA1 group (injected with bleomycin and irradiated with UVA1 of 20 J/cm2), and negative control group (injected only and killed until the end of irradiation). Experimental mouse models of scleroderma were established by subcutaneous injection of 100 μL bleomycin (BLM) at 400 μg/mL into the back of BALB/c mouse once a day for 4 weeks. Phototherapy was performed 3 times weekly for 10 weeks. Thereafter, skin specimens were obtained from the injected or irradiated back of mice, and subjected to an observation on pathological changes of skin tissue and thickness, as well as the measurement of collagen content. Results There was statistical differences between blank control group and model control group in both the skin thickness (t= 4.945, P<0.001) and collagen content (t=3.712, P<0.01). UVAI phototherapy improved the skin sclerosis and reduced the thickness in mouse models, but significant effect was only observed with HD-UVA1 in both the parameters(both P<0.05). There was significant difference among the 3 groups receiving phototherapy in the changes of skin thickness (F=14.853, P<0.01) and collagen content (F= 6.317, P<0.01), and HD-UVAI was significantly more effective than MD-UVA1 and LD-UVA1. Conclusion High-dose UVAI irradiation could significantly reduce the changes in skin thickness and col- lagen content in mouse model of sclerosis induced by bleomycin,which may be related to its inhibition on collagen fiber proliferation and decrease in collagen content.