Optically pure lactic acid that can be prepared by fermentation is one of the important raw materials for biodegradable polymer. Since an economical technique is desired that separates lactic acid from the fermentation broth, we proposed lactate permeation through a poly(vinyl chloride)(PVC)-based membrane containing ionic liquids as a carrier. Lactate was successfully permeated through polymer inclusion membranes (PIMs) containing Aliquat 336, Cyphos IL -101, and -102 as ionic liquids. From the viewpoints of permeation rates and the pH drop of the feed phase, Aliquat 336 was the best ionic liquid. Based on the experimental results, we calculated the overall mass transfer coefficients and evaluated the contribution of membrane resistance to the overall permeation resistance. Furthermore, permeation behavior was explained by the solution-diffusion model. The superior stability of PIMs over the supported ionic liquid membranes was observed for membranes containing Aliquat 336 as a carrier. The PVC-based membrane process containing Aliquat 336 was found to be promising for lactate separation on an industrial scale.