Using astragalus polysaccharides as the core material, sodium alginate as the wall material, a spray coagulation bath method was developed for preparation of astragalus polysaccharides microcapsules, which are uniform particles at the sizes of 100~150μm and insoluble in water. Through phenol-sulfuric acid colorimetry, the drug loading of the microcapsule was measured as 108mg/g, and the embedding rate was 85.7%. A 35-d feeding experiment was conducted on sea cucumbers to evaluate the effects of astragalus polysaccharides microcapsules on resistance against Vibrio splendidus. The basal diet was used as control. Four practical diets were supplemented with 3% blank microcapsule and 1%, 3%, and 5% astragalus polysaccharides microcapsule, respectively (Treatment 1～4). Each diet was randomly allocated to four groups of sea cucumber cultured in 200L fiberglass indoor tanks with circulating seawater and constant aeration. Each tank was stocked with 30 sea cucumbers (initial average weight 30.00±1.00g). After 35 days of feeding with microcapsules or control diet, every group of sea cucumbers were injected into the body wall with 109 CFU/ml live V.splendidus bacterial stock solution at a dose of 0.1 ml per sea cucumber (based on data of 10-day LD50 pre-test). Sea cucumbers in Treatment 3 and 4 showed significantly lower accumulative mortality than the control, or Treatment 1 or 2 (P＜0.05), and no significant difference was observed between Treatment 3 and 4 (P＞0.05).Significant difference was also observed between Treatment 2 and the control (P＜0.05), but no significant difference was observed either between the control and treatment 1, or between treatment 1 and 2 (P＞0.05). According to these results, the oral administration of astragalus polysaccharides microcapsules to A. japonicus at a dose of 3% or 5% enhances the immunity as well as increases disease resistance, and the protective rate may reach 66.67% and 69.44%.