Abalone (Haliotis discus hannai), mostly distributed and maricultured in southwestern coastal areas of South Korea, is recognized as an economically important species in the fishery industry. Abalone intestines are one of the by-products of abalone processing. To investigate abalone intestines as bioactive substances, abalone intestine gastrointestinal digests (AIGIDs) of various molecular weights (MWs) were prepared using in vitro gastrointestinal digestion and an ultrafiltration system, and tested for inhibitory effects against reactive oxygen species (ROS) and oxidative stress in macrophage cells treated with hydrogen peroxide ($H_2O_2$). In our results, among AIGIDs, AIGID-III (MW=5-10 kDa) showed potent inhibitory activities for lipid peroxidation and free radicals. Additionally, the results clearly indicated that AIGID-III treatment could prevent cytotoxic damage of macrophages by $H_2O_2$-induced oxidative stress due to its potent scavenging ability against cellular ROS. These results suggest that AIGIDs may have protective and therapeutic potential for oxidative stress syndromes and immune diseases through ROS inhibition in macrophage cells.