A method of manufacturing a plastic lens, comprising: a step of putting a first curable composition over a forming surface of a first mold substrate having the forming surface for forming a lens surface; a step of spreading the first curable composition over the entire forming surface by pressing the composition with a film to form a first curable composition layer and separating the film from the first mold substrate by a predetermined distance through the formed first curable composition layer; a step of covering an outer edge of the first mold substrate, an outer edge of the film, and an outer edge of a second mold substrate having a forming surface for forming the other surface of the lens with a fastening member to support them and to place the second mold substrate so as to be opposed to the film with being spaced apart from the film by a predetermined distance; a step of injecting a second curable composition into a cavity between the film and the second mold substrate; a step of curing the first curable composition layer and the injected second curable composition to form substrate layers (24, 26) over both sides of the film; and a step of removing the fastening member, the first mold substrate and the second mold substrate to obtain a plastic lens characterized in that, wherein the first curable composition is semi-cured before injecting the second curable composition wherein the storage elastic modulus of the semi-cured first curable composition at 20 °C is 0.01 Pa to 100,000 Pa; or wherein, in the step of putting the first curable composition over the forming surface of the first mold substrate, the viscosity of the first curable composition at 20 °C, measured by a B type viscometer, is 1,000 mPa·s to 100,000 mPa·s. a step of putting a first curable composition over a forming surface of a first mold substrate having the forming surface for forming a lens surface; a step of spreading the first curable composition over the entire forming surface by pressing the composition with a film to form a first curable composition layer and separating the film from the first mold substrate by a predetermined distance through the formed first curable composition layer; a step of covering an outer edge of the first mold substrate, an outer edge of the film, and an outer edge of a second mold substrate having a forming surface for forming the other surface of the lens with a fastening member to support them and to place the second mold substrate so as to be opposed to the film with being spaced apart from the film by a predetermined distance; a step of injecting a second curable composition into a cavity between the film and the second mold substrate; a step of curing the first curable composition layer and the injected second curable composition to form substrate layers (24, 26) over both sides of the film; and a step of removing the fastening member, the first mold substrate and the second mold substrate to obtain a plastic lens characterized in that, wherein the first curable composition is semi-cured before injecting the second curable composition wherein the storage elastic modulus of the semi-cured first curable composition at 20 °C is 0.01 Pa to 100,000 Pa; or wherein, in the step of putting the first curable composition over the forming surface of the first mold substrate, the viscosity of the first curable composition at 20 °C, measured by a B type viscometer, is 1,000 mPa·s to 100,000 mPa·s.