A method of manufacturing plastic metallized 3D circuit includes the steps of providing a 3D plastic main body; performing a surface pretreatment on the plastic main body; performing a metallization process on the plastic main body to deposit a thin metal film thereon; performing a photoresist coating process to form a photoresist protective layer on the thin metal film; performing an exposure and development process on the photoresist protective layer to form a patterned photoresist protective layer; performing an etching process on the exposed thin metal film to form a patterned metal circuit layer; stripping the patterned photoresist protective layer; and performing a surface treatment on the patterned metal circuit layer to form a metal protective layer. With the method, a 3D circuit pattern can be directly formed on a 3D plastic main body without providing additional circuit carrier to thereby meet the requirement for miniaturized and compact electronic devices.