A perfusion bioreactor and a method for using the perfusion bioreactor for performing a continuous cell culture are disclosed. The perfusion bioreactor includes an outer vessel having a housing with a gas permeable membrane, an opening and a cavity; an inner vessel within the cavity; and a lid to cover the opening. A porous membrane within the cavity divides the cavity into inner and outer compartments. A fresh media port extends through the outer vessel or the at least one lid to receive a fresh media tube that has an end located in the inner compartment. A spent media port extends through the outer vessel or the at least one lid to receive a spent media tube that has an end located in the outer compartment. A mixer is within the inner compartment, and the porous membrane is attached to an opening within the inner vessel.