PURPOSE: To provide a method for processing small fishes designed to improve the taste of small fishes and expand the amount of them to be served as foodstuff by packing the peritoneal cavities of small fishes such as smelt with processed food derived from food other than said small fishes.

CONSTITUTION: The peritoneal cavities of small fishes such as smelt or sardines are packed with a processed marine product such as roes other than of said small fishes, laver or sea urchin eggs or a dairy product such as cheese. Thereby, a new taste can be provided (namely, the taste of said small fishes plus that of the processed food packed). An example of the above packing practice is as follows: a nozzle 2 is inserted, through the mouth of a smelt A, into its peritoneal cavity; on pushing a switch 8, a roller 3 is revolved once, 'karashimentaiko' (salted ovary of walleye pollack seasoned with pepper) is pushed by a blades 3a and fed into a cylinder 5; a piston 6 is then pushed, the 'karashimentaiko' being extruded via the nozzle 2, thus packing the peritoneal cavity of the smelt A with the 'karashimentaiko'.