Polymers have been widely accepted as materials for the fabrication of microbioreactor prototypes. In this work, microfabrication strategies namely the micromachining and casting (soft lithography) with the use poly(methyl methacrylate) (PMMA) and poly(dimethylsiloxane) (PDMS) polymers as substrates for fabrications were discussed in details. A step-by-step illustration (including examples on digital prototyping of the microbioreactor by using a computer-aided-design (CAD) software) for the above mentioned micromachining procedures, and discussions on the necessary design considerations were presented as well. In the work, we showed the simplicity of such machining procedures for the fabrication of microbioreactor prototypes. It was confirmed that through micromachining, microbioreactor prototypes can be fabricated by using poly(methyl methacrylate) (PMMA) and poly(dimethylsiloxane) (PDMS) polymers with high precision (down to one tenth of mm). It was also demonstrated that the processing time for the fabrication of the microbioreactor prototypes was in the order of few hours and maybe days for a complex reactor design.