The Zostera marina ethanolic extract (ZMEE) was tested in this study to investigate the anti-inflammatory activity in LPS-induced RAW 264.7 cells and mouse model. Nitric oxide production and inducible nitiric oxide synthase expression in cells treated with ZMEE was reduced significantly in a dose-dependent manner. Similarly, the secretion of pro-inflammatory cytokines such as interleukin (IL)-6, IL-1β, and TNF-α was inhibited markedly. In addition, the expression of nuclear factor kappa B (NF-κB) and the phosphorylation of JNK, ERK, and p38 MAPKs was suppressed by ZMEE as well. In vivo test, ZMEE attenuated the croton oil-induced mouse ear edema and there were no mortalities in mice administered 5,000 mg/kg body weight of ZMEE during the observation periods. The results in photomicrograph of mice ear tissue showed the reduction of dermal thickness and the number of infiltrated mast cells. These results indicate that ZMEE inhibits the production of LPS-induced pro-inflammatory mediators, suggesting that ZMEE may be a potential material for anti-inflammatory therapies.