A FUEL FOR A DIESEL ENGINE IS PRODUCED BY USING A FISH WASTE OIL OR A MIXTURE OF A VEGETABLE WASTE OIL AND THE FISH WASTE OIL WHICH HAVE CONVENTIONALLY BEEN WASTED AS A STRATING MATERIAL . FISH OIL ( VIRGIN OIL OR FISH WASTE OIL) OR A MIXTURE OF THE FISH OIL AND VEGETABLE OIL ( VIRGIN OIL OR VEGETABLE OIL ) (HEREINAFTER REFERRED TO AS "STARTING MATERIAL") IS SUBJECTED TO STIRRING TREATMENT WHILE INTRODUCING OZONE, AND AN OXIDATION-REDUCTION AGENT AND A POLYMERIZATION INHIBITOR ARE ADDED DURING THE STIRRING TREATMENT. MOREOVER , IT COMPRISES THE RESPECTIVE STEPS OF A FIRST TREATMENT STEP IN WHICH A STIRRING TREATMENT IS CARRIED OUT WHILE INTRODUCING OZONE-MENTIONED STARTING MATERIAL, AND AN OXIDATION-REDUCTION AGENT AND A POLYMERIZATION INHIBITOR ARE ADDED DURING THE STIRRING TREATMENT, A SECOND TREATMENT STEP IN WHICH THE MATERIAL OBTAINED IN THE ABOVE-MENTIONED FIRST STEP IS FILTERED AND STIRRING TREATMENT IS FURTHER CARRIED OUT WHILE INTRODUCING OZONE AGAIN, AND A STEP OF INTRODUCING A VEGETABLE ADDITIVE TO THE RESULTING MATERIAL BY THE SECONG TREATMENT STEP.