The diagnostic of several diseases can be performed by analyzing the blood plasma of the patient. Despite the extensive research work, there is still the need to improve the current low-cost fabrication techniques and devices for the separation of the plasma from the blood cells. Microfluidic biomedical devices have a great potential for that process. Hence, a microfluidic device made by micromilling and sealed with the oxygen plasma technique was tested by means of two different blood analogue fluids. The device has four microchannels having similar geometries but with different channel depths. A high-speed video microscopy system was used for the visualization and acquisition of the flow of the analogue fluids throughout the microchannels of the device. Then, the separation of particles and plasma was evaluated using the software ImageJ by measuring and comparing the grey values at the entrance and at the exit of the channel. The device has shown a significant reduction of the amount of cells between the entrance and the exit of the microchannels. No major influences were found from the depth of the channels and size of the particles on the separation process. However, it was found that flow rate has affected the separation results where the best results were obtained for a flow rate of 100 μL/min. Although these results are promising, further analysis and optimizations of the microfluidic devices will be conducted in future works, as well as, the comparison between devices sealed using different methods, such as, the solvent bonding technique.