Abstract: Objective To investigate the possible therapeutic mechanism of narrow-band UVB （NB-UVB） plus tazarotene in psoriasis vulgaris. Methods Patients with psoriasis vulgaris were divided into UVB group （n = 27） and placebo group （n = 24）. The patients in UVB group were given topical tazarotene to lesions in the left side of body, and placebo in the right side, then received UVB irradiation; tazarotene was applied once per night and UVB was given once every other day. The placebo group were only given topical placebo to lesions without irradiation. Immunohistochemistry and in situ hybridization were used to detect the protein and mRNA expressions of tazarotene induced gene-2 （TIG2） in the psoriatic lesions at the baseline, and after 2, 6 weeks of treatment. Results Before treatment, there was almost no expression of TIG2 in psoriatic epidermis. After treatment with NB-UVB alone, TIG2 was slightly expressed in parakeratotic stratum corneum and the upper layer of stratum spinosum in 2 weeks, in the upper and middle layers of stratum spinosum in 6 weeks. After combination treatment with NB-UVB and tazarotene, TIG2 was expressed throughout the whole stratum spinosum and basal layer with an increase in the upper layer compared with the middle and lower layers in 2 weeks, throughout the whole layer of epidermis that had become thinner in 6 weeks. TIG2 was firstly expressed in parakeratotic stratum corneum, then in the upper layers, middle and lower layers of stratum spinosum, finally in the basal layer after the treatment with NB- UVB alone or in combination with tazarotene, and the combination with tazarotene accelerated this expression process. Conclusion The synergy between NB-UVB and tazarotene in the treatment of psoriasis may be related to the up-regulation of TIG2 expression in psoriatic epidermis.