Abstract: A method for producing 3-mercaptopropionic acid and methods using same for producing a carbonic acid ester compound having a mercapto group and a thiourethane-based optical material. The present invention improves a process during the production of 3-mercaptopropionic acid, significantly increases yield, and reduces the temperature and time during vacuum distillation, thereby preventing the destruction of a product and significantly increasing productivity. The present invention allows high-purity 3-mercaptopropionic acid having an excellent color to be finally yielded; accordingly, by using same, a high-purity carbonic acid ester compound having an excellent color and a mercapto group can be inexpensively obtained. A thiourethane-based polymeric composition and a thiourethane-based optical material obtained by polymerizing same can likewise be inexpensively obtained by using said carbonic acid ester compound.