Ecklonia cava (EC) is a brown alga that evidences radical scavenging activity, bactericidal activity, tyrosinase inhibitory activity, and protease inhibitory activity. However, its anti-allergic effects remain poorly understood. In the current study, we attempted to determine whether pretreatment with EC induces a significant inhibition of asthmatic reactions in a mouse asthma model. Mice sensitized and challenged with ovalbumin (OVA) evidenced typical asthmatic reactions, as follows: an increase in the number of eosinophils in bronchoalveolar lavage fluid; a marked influx of inflammatory cells into the lung around blood vessels and airways, and airway luminal narrowing; the development of airway hyperresponsiveness; the detection of tumor necrosis factor-alpha (TNF-alpha) and Th2 cytokines, including IL-4 and IL-5 in the bronchoalveolar lavage (BAL) fluid; and the detection of allergen-specific immunoglobulin E (IgE) in the serum. However, the administration of EC extract prior to the final airway OVA challenge resulted in a significant inhibition of all asthmatic reactions. We also demonstrated that EC extracts treatment resulted in significant reductions on matrix metalloproteinase-9 (MMP-9) and Suppressor of cytokine signaling-3 (SOCS-3) expression and a reduction in the increased eosinophil peroxidase (EPO) activity. The treatment of animals with EC extracts resulted in a significant reduction in the concentrations of the Th2 cytokine (IL-4 and IL-5) in the airways, without any concomitant increase in the concentration of Th1 cytokines. These findings indicate that EC extracts may prove useful as an adjuvant therapy for allergic airway reactions via the inhibition of the Th2 response. Accordingly, this study may provide evidence that EC extract performs a critical function in the amelioration of the pathogenetic process of asthma in mice.