PROBLEM TO BE SOLVED: To provide a method for making a useful component to be taken into a body of an aquatic organism efficiently without giving any external injury on the aquatic organism, the method being capable to reduce the occurrence of death of the aquatic organism after the uptake.SOLUTION: A method for making a useful component to be taken into a body of an aquatic organism includes: a process for immersing the aquatic organism in a protease solution; and a process for immersing the aquatic organisms in a liquid containing the useful component after that. This invention allows the useful component to be taken into the majority of aquatic organisms effectively and inexpensively.