In this paper, a particle counting system using a CMOS image sensor is demonstrated. The system utilizes a linear photodetector array as a detection element. Therefore, the particles are detected by multiple detectors simultaneously, in contrast to a single detector in conventional particle counting devices, while maintaining the sensitivity. Another advantage of the proposed system is that particles are detected across the full-channel width which removes the need for a particle-focusing method. Also, the proposed system can easily be integrated with a microfluidic chip fabricated on a transparent substrate, as the counting system is attached under the microchannel and counts the particles optically. Detection of polystyrene microbeads has been tested at a flow rate of 5.15mm s -1. For 21 measurements, the proposed system showed an average count error of 4.56% and a standard deviation of 3.06% using a proposed compensation algorithm. Potentially, the proposed system can detect even smaller particles simply by utilizing a higher resolution CMOS image sensor.