Plasma medicine is an emerging novel therapeutic field. It has been reported that plasma can kill bacteria, promote wound healing and induce apoptosis of tumor cells. However, the effects of plasma on immune cells and immune related skin diseases have not been well studied. In this study, we demonstrated that non-thermal atmospheric plasma (NTP) treatment could inhibit psoriasis-like skin inflammation in mice. NTP treatment in imiquimod-induced psoriasis-like mouse skin inhibited increases in epithelial cell thickness and expression of pro-inflammatory molecules compared to ones without the NTP treatment. In addition, differentiation of Th17 cells, an important cell type for pathogenesis of psoriasis, was inhibited in the NTP-treated mouse lymph nodes. It was also demonstrated that liquid type plasma (LTP), which is also known as indirect plasma, inhibited Th17 cell differentiation in vitro. Other in vitro experiments showed that LTP inhibited bone marrow-derived dendritic cell activation. Interestingly, LTP enhanced PD-L1 expression in HaCaT cells, suggesting that NTP may inhibit unwanted over-activation of T cells through increased PD-L1 expression. Taken together, these results suggest that NTP may be used in treatment of CD4+ T cell-mediated autoimmune diseases such as psoriasis.