To provide a method for treating a cracked oil which is obtained by catalytic pyrolysis for waste plastic from which a chlorine-containing resin, a polyester resin, or the like, are removed and which can be converted to a high-quality heavy liquid fuel which can be used for fuel oil for a boiler and diesel fuel oil.

In the method for treating waste plastic cracked oil, shaped solid materials are produced from separated waste plastic principally containing a polyethylene resin, a polypropylene resin, and a polystyrene resin, liquid fuel is obtained consisting of a 10-30C aromatic compound and an aliphatic compound by catalytic pyrolysis reaction for the shaped solid materials and a catalyst of zeolite-based particles in a catalytic reaction vessel under the conditions of high-temperature range and a non-oxygen state, and neutralization treatment with alkaline components and removal treatment of impure fine particles with a specific filter are performed.