A plastic optical fiber comprising a fluorine-containing core polymer consisting essentially of 1) a group (A) of repeating units having a cyclic structure represented by general formula (I) and/or general formula (II); or 2) the group (A) above and group (B) of repeating units represented by general formula (III) wherein the content of the group (A) in the core polymer is at least 80 wt %; and a clad copolymer of perfluoro(2,2-dimethyl-1,3-dioxole) and at least one other ethylenically unsaturated monomer having a refractive index below that of the core polymer. ##STR1## (wherein n is 1 or 2)--CF.sub.2 --CFX (III)(wherein X is F, Cl, O--CF.sub.2 CF.sub.2 CF.sub.3, O--CF.sub.2 CF(CF.sub.3)OCF.sub.2 CF.sub.2 SO.sub.2 F, or O--CF.sub.2 CF.sub.2 CF.sub.2 COOCH.sub.3)This plastic optical fiber has heat-resistance and very few water-absorbing properties, and can transmit not only visible rays but also rays having wavelengths in the near infrared region.