A purification of lactic acid from a fermentation broth was carried out by molecular distillation following the associated calcium precipitation and solvent extraction. Response surface methodology was adopted to investigate the independent experimental parameters. Under the optimal distilling temperature of 367.1 K and operation pressure of 24.5 Pa, lactic acid purity, and yield can reach 92.39% and 74.09%, respectively, with only a single-pass distillation. A multi-pass distillation procedure was further designed to obtain lactic acid with a higher purity about 95.6%. Given the small scale of the laboratory device, a simplified mathematical strategy for scale-up was introduced to serve a practical production.,