In this study, the clogging mechanism of poly( styrene) particles in the flow through a single micro-pore was investigated. Together with the microscopic observation, the pressure drop was also measured. The pressure drop fluctuated according to the amount of particles deposited inside the channel. When the particles deposited and blocked the channel, the channel was clogged and the pressure drop increased sharply. During the clogging process, the particles were often detached by the flow, and interesting behaviors, such as "rolling" and "stick and detach", were found to be the key factors that determine whether the clogging completely occurs or not. Above a certain flow rate, the channel was not clogged and the pressure drop did not increase further. The particles deposited in the upstream had an influence on the flow path. When the particles were deposited in the upstream, the flow detoured and the vortex was formed. The effect of viscosity was examined by controlling the concentration of glycerol solution. As the viscosity and the flow rate increased, the shear stress applied to the particles became larger and it was more difficult for the particles to get accumulated. The normalized clogging pressure drop decreased exponentially with shear stress. It was unity above a certain shear stress, in which the particles did not clog the channel completely.