PURPOSE: To manufacture a multi-layer plastic fuel tank to be able to improve the barrier performance of gasoline up to the level of 0.2gr/day or lower.

CONSTITUTION: The tank wall section of a blow molding fuel tank is composed of five layers of three kinds, namely a high density polyethylene layer, a bonding material layer, a polyamide layer, a bonding material layer and a high polyethylene layer, and (1) the high density polyethylene layer is composed of the combination of a polymer non-compatible with high density polyethylene and high density polyethylene, and alkyl carboxyl substituted polyolefin, and the non- compatible polymer exists in the form of a number of thin layers two- dimensionally and in parallel in a continuous matrix phase of high density polyethylene. A layer in which the alkylcarboxyl substituted polyolefin exists interlaminarly is formed, or (2) a bonding material layer composed of the combination of the bonding material and a polymer non-compatible with the bonding material and existing in the form of a number of thin layers of the non- compatible polymer two-dimensionally and in parallel on a continuous matrix phase of bonding material is formed.