Abstract： Objective To investigate the therapeutic effect of narrow band ultraviolet B ( NB VUB)and its influence on the expression of IL23/Th17 axis in peripheral blood of patients with Psoriasis vulgaris,and to further explore the mechanism of action of NB UVB.Methods Forty - eight cases of Psoriasis vulgaris were treated with NB-UVB irradiation for 20 times,the therapeutic effect was evaluated by the Psoriasis Area and Severity Index (PASI) scores.Peripheral blood was obtained from normal healthy controls and patients with Psoriasis vulgaris before and after NB-UVB irradiation.Three color flow cytometry was carried out to quantify Thl7 cells,and ELISA was used to examine the levels of serum IL17 and IL23.Results The mean PASI scores were significantly decreased after treatment with NB UVB irradiation[ (8.12±4.05)score vs (3.98±2.03) score,P＜0.01 ].Levels of Th17[ (2.78 ± 1.93)％ vs (0.98±0.56)％ ],IL-17[ (23.85±7.98) pg/ml vs (6.53±4.26) pg/ml] and IL-23 [ (29.73 ± 12.08)pg/ml vs ( 16.73±8.91 )pg/ml] were significantly higher in patients with Psoriasis vulgaris than that in healthy controls ( P ＜0.01 ).After treatment with NB-UVB irradiation,levels of Th17 [ ( 1.13 ± 0.51 ) ％ ],IL-17 [ ( 8.03±5.01 )pg/ml ],and IL-23 [ ( 17.03 ± 9.85 )pg/ml ] were significantly decreased than before ( P ＜ 0.01 ),and were positively correlated with PASI ( P ＜0.05).Conclusions NB-UVB may affect IL23/IL17 to achieve its therapeutic effect on patients with Psoriasis vulgaris.