Physical cues are critical for regulating the differentiation of myoblasts in vitro, and mechanical and electrical stimulations are the most effective ones. Therefore, we developed a multifunctional bioreactor to simultaneously perform these two stimulations. Conductive polypyrrole (PPy) was prepared on a flexible polydimethylsiloxane (PDMS) substrate to form a highly stretchable conductive PPy/PDMS membrane. To promote PPy deposition, surfaces of PDMS were etched by NaOH to increase roughness and functionality. These PPy/PDMS membranes maintained electrical resistance lower than 20 kΩ when the tensile strain was lower than 35 % and was reliable for repeated cyclic stretching at 10 % of tensile strain. These PPy/PDMS membranes were dark but transparent and thus were feasible to directly monitor cells on their surfaces. Therefore, we applied PPy/PDMS membranes to build a bioreactor for the application of electrical and mechanical stimulations. Cyclic stretching effectively promoted myotube formation. Furthermore, C2C12 cells under cyclic stretching were aligned perpendicular to the stretching direction, so the formed myotubes were parallel to each other. The combination of cyclic stretching and electrical stimulation demonstrated synergistic effects and myotube alignment can be preserved. Overall, this bioreactor constructed by PPy/PDMS membranes can perform two diverse stimulations and is potential for muscle tissue engineering applications.