PURPOSE: To obtain a frozen fish for boiling hard with soy, preservable for a long period and capable of readily preparing fish boiled hard with soy in a microwave oven, etc., by preparing a fish and seasoning, removing viscera, boiling the fish with the above-mentioned seasoning and freezing the resultant fish.

CONSTITUTION: Viscera of a fish, such as mackerel, are removed and then the head is removed to divide the fish into three pieces of the backbone and two slices. Thereby, bones are removed. The slices after the afore-mentioned dividing into the three pieces of the backbone and two slices are skinned. On the other hand, the head and bones removed from the fish are placed in boiling water and taken out to provide a broth. Sugar, soy sauce, 'MIRIN' [sweet SAKE (Japanese rice wine)], SAKE, etc., are then blended in the broth to prepare a seasoning, which is used to boil and cook the above- mentioned fish divided into the three pieces of the backbone and two slices. The afore-mentioned seasoned fish is subsequently vacuum-packed with a heat-resistant PE bag, etc., and then frozen. As a result, the resultant seasoned and frozen fish can be heated in, e.g. a microwave oven, to readily prepare a fish for boiling hard with soy. The above-mentioned frozen fish for boiling hard with soy can be stored in a refrigerator, etc., and preserved for a long period.