Up-regulation of selected matrix metalloproteinases (MMPs) such as MMP-9 contributes to inflammatory processes during the development of various skin diseases, such as atopic dermatitis. In this study, we examined the effect of a cell-permeable superoxide dismutase (Tat-SOD) on TNF-${alpha}$-induced MMP-9 expression in human keratinocyte cells (HaCaT). When Tat-SOD was added to the culture medium of HaCaT cells, it rapidly entered the cells in dose- and time-dependent manners. Tat-SOD decreased TNF-${alpha}$-induced reactive oxygen species (ROS) generation. Tat-SOD also inhibited TNF-${alpha}$-induced NF-${kappa}B$ DNA binding activity. Treatment of HaCaT cells with Tat-SOD significantly inhibited TNF-${alpha}$-induced mRNA and protein expression of MMP-9, as measured by RT-PCR and Western blot analysis. In addition, Tat-SOD suppressed TNF-${alpha}$-induced gelatinolytic activity of MMP-9. Taken together, our results indicate that Tat-SOD can suppress TNF-${alpha}$-induced MMP-9 expression via ROS-NF-${kappa}B$-dependent mechanisms in keratinocytes, and therefore can be used as an immunomodulatory agent against inflammatory skin diseases related to oxidative stress.