Since plasma proteins are varied depending on diseases states, its continuous monitoring has been considered as effective diagnostic tool. In this study, a simple and efficient method for separate plasma and red blood cells (RBCs) from blood sample is proposed with a microfluidic device. To separate plasma in continuous way, microfluidic guiding channel is designed by connecting two channels with different heights in parallel, and employs inertial force and Zweifach–Fung bifurcation law. Due to its unique geometry, most RBCs flowed inside wall region with higher height. Then, plasma is collected from center region with lower height. As a result, the efficiency of plasma separation is achieved over 90 %. Furthermore, it is remained constant, even up to high value of 40% hematocrit. In the near future, the proposed method will be integrated with a lab-on-a-chip for diagnosing diseases.