A method is provided for manufacturing a processed marine plant food. It comprises (a) crushing marine plants into small pieces； (b) heating the marine plant pieces together with alkaline salts at a temperature of from 40 to 80° C. while stirring in a vacuum stirrer to generate a marine plant paste； and (c) gelling the marine plant paste with a metal ion solution of di- or higher valency to form a marine plant jelly. When manufactured by the method, the marine plant food retains its characteristic taste, flavor and color, without their components beneficial to the body being lost or denatured.
