PURPOSE: To obtain a plastic fuel tank improved in fire resistance without using thermal insulation plate in the bottom part of the fuel tank by covering the outermost shell layer of the fuel tank with a fire-retardant foam layer.

CONSTITUTION: A fire-retardant multi-layer plastic fuel tank 1 consists of a fire-retardant plastic foam layer formed on an outermost shell layer 5 and a HDPE layer 4 or HDPE/adhesive agent/PA/HDPE layer. The foam layer is formed of plastic foam and polyethylene foam in combination with halogen containing organic compound, chloric halogen containing organic compound and halogen free inorganic compound as flame retardant. By using azo and nitroso organic foaming agent and through blow molding process, a fire- retardant plastic foam layer is formed on the outermost shell layer 5 simultaneously and then foaming treat is effected.