The ability to characterize hematopoietic cells quickly and reliably is critical in precision medicine. Analysis of hematopoietic cells will lead to the diagnosis of various diseases, including infectious diseases and cancer. Microfluidic devices provide label-free, time-efficient, and quantitative analysis in this regard. A microfluidic system is provided in this work to separate Red blood cells (RBCs) from B-Lymphocytes (B-Cells). One of the ways for manipulating and separating micron-sized particles is dielectrophoresis (DEP). Dielectrophoretic manipulation of red blood cells (RBC) and B-Lymphocytes (B-Cells), with diameters of 2.8 μm and 3.29 μm, respectively, is studied. The simulation results of a microfluidic device with a sidewall electrode are shown. RBCs could be separated with 98 % efficiency from B-Cells at an applied voltage ±0.06 V with a frequency and flow rate of 10 kHz and 1.5 μL/s, respectively.