<;P>;PROBLEM TO BE SOLVED: To provide a macrophage-activating agent, interleukin 12-production-inducing agent and immunostimulant. <;P>;SOLUTION: This macrophage-activating agent, interleukin 12-production-inducing agent and immunostimulant contains an acidic mucopolysaccharide produced by marine bacteria as an active ingredient. The molar ratio of constituting saccharides of the acid mucopolysaccharides is (2:1:1:1) recurring units of N-acetyl-D-galactosamine:D-glucuronic acid:N-acetyl-L-galactosamine:pyruvic acid respectively, and the mean molecular weight of the mucopolysaccharide is 1,000,000 to 1,500,000. The marine bacteria is Pseudomonas sp WAK-1 strain or its mutated species. <;P>;COPYRIGHT: (C)2006,JPO&NCIPI