Disclosed is a plastic heat exchanger in which, when a heat exchanger tube of the plastic heat exchanger is coupled to a header, the heat exchanger tube and a junction portion of the header are melted and pressed simultaneously through a heat fusion jig including a fusion portion and a fusion valley so as to secure reliability against leakage of refrigerant, and a method of manufacturing the same, by which the plastic heat exchanger can be mass-produced at low fabricating cost through simple processes. The present invention provides a method of fabricating a plastic heat exchanger, comprising a step of melting and pressing a plastic heat exchanger tube and a junction of a header by using a heat fusion jig, and a plastic heat exchanger fabricated by the method, thereby securing reliability against leakage of refrigerant, having heat exchange performance more excellent than or equal to a metallic heat exchanger and also mass-producing the plastic heat exchanger at low fabricating cost through simple processes.