Abstract： Objective To investigate the role of phosphorylated extracellular signal-regulated kinase (p-ERK), mitogen-activated protein kinase (MAPK)/ERK kinase (MEK), and nuclear factor-κB (NF-κB) in the pathogenesis of psoriasis vulgaris. Methods Immunohistochemistry and Western blot were used to detect the expression of p-MEK, p-ERK and p-NF-KB in tissue samples from 30 patients with psoriasis vulgaris and 15 normal human controls. The average optical density of immunostaining and relative grey scale of immuno-bloting were calculated. Results The average optical density of immunostaining for p-MEK, p-ERK and p-NF-KB was 0.36 ± 0.03, 0.36 ± 0.04 and 0.26 ± 0.04, respectively in lesion samples of psoriasis, significantly higher than that in normal control tissue (0.22 ± 0.02, 0.18 ± 0.03 and 0.16 ± 0.03, all P < 0.01). A significant increase was also observed in the relative grey scale of p-MEK, p-ERK and p-NF-κB in psoriatic lesions compared with the normal controls (1.41 ± 0.14 vs 0.54 ± 0.10, 2.35 ± 0.34 vs 1.86 ± 0.12, 1.07 ± 0.15 vs 0.87 ± 0.08, all P < 0.01). Conclusions The expressions of p-MEK, p-ERK and p-NF-κB are enhanced in lesions of psoriasis vulgaris, and the abnormal activation of upstream and downstream molecules in the MAPK signaling pathways might be involved in the pathogenesis of psoriasis.