An optical material, particularly a plastic lens for spectacles, which absorbs almost all UV rays of up to around 400 nm or so and is not too yellow in color, is obtained by adding 2-(2-hydroxy-4-octyloxyphenyl)-benzotriazole to a diethylene glycol bisallylcarbonate monomer, a (thio)urethane monomer or an episulfide monomer, mixing them, and polymerizing the monomer.