The present application relates to a microorganism of the genus Saccharomyces producing lactic acid and a method for preparing lactic acid using the same. More specifically, the present application relates to a microorganism of the genus Saccharomyces producing lactic acid, wherein the microorganism is modified to weaken or inactivate the activity of pyruvate decarboxylase (PDC) compared to its endogenous activity, to introduce the activity of ATP-citrate lyase (ACL), and to enhance pyruvate biosynthetic pathway compared to its endogenous biosynthetic pathway, and a method for producing lactic acid using the microorganism.