A heat-resisting plastic optical fiber which excels in heat resistance and mass production and a manufacturing method thereof. The heat-resisting plastic optical fiber has a core which consists of transparent resin, and clad coated on the outer periphery of the core, which consists of the resin whose refractive index is lower than that of core. Precursor of material for the core material consists of the mixture of a group of monomers which contain polyfunctional monomer and transparent thermoplastic polymer.