Abstaract Separation and concentration of micro and nanoparticles are of particular importance in many biomedical applications. Isolation and identification of virus nanoparticles from whole blood containing white and red blood cells are crucial for the rapid diagnosis of infectious diseases such as HIV, Ebola, and SARS as well as emerging infectious diseases such as influenza that pose serious health challenges. In this study, a spiral inertial microfluidic device is described that can separate polystyrene particles with a diameter equivalent to viruses from particles with a diameter equivalent to red and white blood cells based on their size. This device, without using any external force and only with the help of inertial lift and drag forces on particles of different sizes, leads to differences in their transfer rate within the cross-section of the microchannel and ultimately separates them from each other. Large particles with diameters equivalent to red and white blood cells, under the influence of the dominant forces of inertia and Dean drag force due to the microchannel helical geometry, equilibrate in a certain position close to the inner wall of the microchannel, while 250 nm small particles equivalent to the diameter Viruses, as a result of Dean drag forces on them, are trapped in Dean vortices formed inside the cross-section of the channel and transmitted to the outer wall of the microchannel. Finally, due to the dual role of Dean forces in the concentration of micro particles in a specific position close to the inner wall of the channel and the transfer of submicron particles from the inner half of the microchannel cross-section to its outer half at the channel outlet, two separate streams of particles are formed and Collected in two separate outputs. The spiral microchannel consisting of 4 loops, 180 ?m wide, and 60 ?m high, at Dean Number 1.6, a total flow rate of 125 ?L/min and 1:2.3 ratio of the flow rate between solution containing particles and sheath flow was successfully able to separate 250 nm submicron particles with an efficiency of 87%, and purity of 100% from 7 and 10 ?m particles. Modeling results in confirmation with laboratory data are also presented in this research. The flat and uncomplicated structure of this separator makes it relatively simple to integrate with other laboratory microfluidic systems on the chip for continuous particle separation. Keywords : Inertial microfluidic devices, Particle separation, Dean flow, Sheath flow