Atopic dermatitis (AD) is caused by both dysregulated immune responses and an impaired skin barrier. Although leukotriene B4 (LTB4) is involved in tissue inflammation that occurs in several disorders, including AD, therapeutic strategies based on LTB4 inhibition have not been explored. Here we demonstrate that progression of an AD-like skin disease in NC/Nga mice is inhibited when docosahexaenoic acid (DHA)/eicosapentaenoic acid (EPA) is administered together with FK506. Treatment with DHA/EPA and FK506 decreases the clinical score of dermatitis in NC/Nga mice and lowers local LTB4 concentrations. The treatment also suppressed the infiltration of T cells, B cells, eosinophils and neutrophils, and promoted reduced serum IgE levels. Secretion of IL-13 and IL-17A in CD4⁺ T cells was lower in DHA/EPA- and FK506-treated mice than in mice treated with FK506 alone. The inhibition of disease progression induced by DHA/EPA was reversed by local injection of LTB4, suggesting that the therapeutic effect of DHA/EPA is LTB4-dependent. Our results demonstrate that treatment of AD with DHA/EPA is effective for allergic skin inflammation and acts by suppressing LTB4 production. J. Med. Invest. 63: 187-191, August, 2016