The present invention provides a plastic optical component. The plastic optical component has superior characteristics including lightweightness, low cost and suitability for mass production. The plastic optical component exhibits superior moisture barrier quality while experiencing no uneven refractive index profile in their interior even if they are subjected to the effect of water in the environment. The plastic optical component has a moisture-proof coating formed at least on the surfaces in contact with the outside air. During the transient period from the time when the water absorbencies of the surface and central portions of the component began to change on account of an environmental change until the time when they reach the saturated water absorbencies, the difference between the refractive indices of the surface and central portions of the component is no more than 0.0002.