The performance of membrane reactors, in which the enzymatic Synthesis of glucose 6-phosphate from glucose and polymer-bound cofactor ATP with simultaneous regeneration of polymer-bound ATP from polymer-bound ADP and acetyl phosphate are performed, was analyzed theoretically. Simplified and realistic models for two different membrane reactors, a plug-flow-type membrane reactor (PFMR) in a diffusion mode and a continuous stirred tank reactor-type membrane reactor (CSTMR) in a filtration mode, were presented and compared theoretically. The results showed that the reactor performance mainly depends on the operating conditions and that, in most cases, the PFMR in a diffusion mode was found to be superior to the CSTR in a filtration mode. This study provides useful information for selecting and optimizing of the reactor for enzymatic reactions requiring cofactors.