We present here an innovative three dimensional microfabrication technology coupled with mass transport simulation to enable the design and fabrication of advanced microbioreactors. The core of our microfabrication technology is a high-resolution projection micro stereo lithography (PμSL) using a spatial light modulator as the dynamic mask. This unique technology provides a parallel fabrication of highly complex 3D microstructures. In this work, a set of polyethylene glycol) bioreactors are demonstrated with PμSL technology. Supported by the results of our numerical study, the precisely controlled channel density (>150/mm 2) in the polymer matrix and improved transport of nutrient and oxygen through advection and diffusion represent the key advantages of the microfabricated bioreactors to the traditional foam and hollow fiber based bioreactors. Development of this 3D microfabricated bioreactors are expected to have direct impact on applications such as analyte controlled and modulated drug and protein delivery, drug targeting, tissue engineering, and micro- or nano-devices.