During cancer metastasis, circulating tumor cells (CTC) are exposed to biomechanical forces such as hydrostatic pressure and shear stress in their microenvironments. While these factors play an important role in the heterogeneity of the cancer cell, they also greatly affect cell viability. In this study, a circulating microfluidic bioreactor was developed to mimic the hemodynamic shear stress that CTC cells are exposed to during the metastasis process and theoretical calculations were carried out for the velocity, wall pressure and shear stresses of the microfluidic bioreactor. After that, the viability of MDA-MB-231 breast cancer cells at increasing hemodynamic shear stresses and circulation times (6, 12, and 24 hours) at three different flow rates (6, 12 and 24 hours), was investigated via MTT test and live/dead assay. Experimental results showed that cell viability decreased as the hemodynamic shear stress and circulation time on cells increased compared to breast cancer cells cultured in static conditions. Also, it has been reported that cell viability decreases up to 20% in high hemodynamic shear stress (66 dyn cm(-2)) and long circulation time (24 hours). With this circulating microfluidic bioreactor, the viability of cancer cells in hemodynamic flow conditions can be evaluated as well as phenotypic and genotypic changes can be examined.