As a method by which failed products of hard-coated plastic lenses, especially hard-coated high-refractive-index plastic lenses can be regenerated to be in a re-usable condition, plastic lenses coated with a hard coat consisting essentially of an organopolysiloxane compound and an inorganic oxide, are contacted with an aqueous solution of a silicate and/or a phosphate. For example, an aqueous solution of 30% trisodium phosphate heated at 50° C. is sprayed over hard-coated plastic lenses for 5 minutes. The hard coat is removed from the lenses, while the surface of the coat-removed lenses is not roughed. The coat-removed lenses are re-usable.