Disclosed is an optical fiber wherein a monomer for a core portion contains trichloroethyl methacrylate as a main component, said trichloroethyl methacrylate being excellently transparent and very flexible. The optical fiber enables high-speed communication. Specifically disclosed is an optical fiber composed of a core portion and a cladding portion arranged around the core portion, wherein the core portion is mainly composed of a polymer of a monomer that contains not less than 70% by weight of trichloroethyl methacrylate (TCEMA) and the cladding portion is mainly composed of a polymer of a monomer that contains not less than 20% by weight of methyl methacrylate (MMA). Also specifically disclosed is an optical fiber composed of a core portion and a cladding portion arranged around the core portion, wherein the core portion is mainly composed of a polymer of a monomer that contains not less than 70% by weight of TCEMA and the outer circumference of the cladding portion is covered with a plastic that contains a polycarbonate as a main component.
