Objective To evaluate the therapeutic effect of narrow band-ultraviolet B (NB-UVB) alone or in combination with interferon-alpha-2b (INF-alpha-2b) for mycosis fungoides (MF),and to assess the correlation between the therapeutic effect and peripheral blood regulatory T (Treg)/T helper type 17 (Th 17) cells.Methods Thirty-three patients with stage ⅠA to ⅡA MF were randomly divided into two groups:NB-UVB group (n =15) receiving NB-UVB radiation alone,combined group (n =18) treated with NB-UVB radiation and intramuscular injection of INF-alpha-2b.Ten healthy volunteers were selected as the control group.Peripheral blood samples were collected before and 9 months after the start of treatment.Flow cytometry was performed to determine the percentages of Treg cells and Th17 cells.Statistical analysis was carried out by using t test,one-way analysis of variance,and Fisher's exact test.Results The average treatment duration was 9 months among these patients.Therapeutic outcomes were significantly better in the combined group than in the NB-UVB group (P =0.023).Among the 15 patients in the NB-UVB group,6 achieved complete remission,3 partial remission,6 showed no response;of the 18 patients in the combined group,12 experienced complete remission,5 partial remission,and 1 showed no response.Before the treatment,the percentages of both Treg and Th17 cells in peripheral blood were significantly higher in the NB-UVB group and combined group than in the control group (both P ＜ 0.05),but similar between the NB-UVB group and combined group (both P ＞ 0.05).After the treatment,the percentages of both Treg and Th17 cells in the NB-UVB group and combined group significantly decreased compared with those before the treatment,but were still higher than those in the control group (both P ＜ 0.05).Additionally,the degree of decrease in the percentages of Treg and Th17 cells was significantly greater in the combined group than in the NB-UVB group (both P＜ 0.05).The seven patients with no response also showed a significant decrease in the percentage of Treg cells (P ＜ 0.05),but no obvious changes in that of Th 17 cells (P ＞ 0.05) after the treatment.Conclusions The therapeutic effect of NB-UVB radiation combined with intramuscular INF-alpha-2b is superior to that of NB-UVB radiation alone for MF,which may be associated with the degree of decrease in peripheral blood Treg and Th 17 cells.