Embodiments relate to a polythiol composition for a plastic optical lens and a polythiourethane-based plastic optical lens prepared therefrom. In the embodiments, a first polythiol compound having mercapto groups only as a hydrogen-bondable functional group and a second polythiol compound having mercapto groups as a hydrogen-bondable functional group and a hydrogen-bondable functional group other than a mercapto group are used in an appropriate amount. Thus, not only is it possible to control the viscosity of a polymerizable composition at the initial stage of polymerization at a low temperature of 5 to 15° C. and to stabilize the rate of increase in the viscosity of the composition and the reaction rate thereof, but also the change in the viscosity at a low temperature is low, thereby preventing the generation of striae, bubbles, and the like. Further, various plastic lenses such as eyeglass lenses, camera lenses, and the like having excellent appearance characteristics (without striae and bubbles) and excellent optical characteristics can be obtained from the composition.