An experimental method is proposed to determine the total collection efficiency of a cyclone. An optical technique is utilized to measure and calculate the total collection efficiency by integrating the area below the size distribution curve upstream and downstream of the cyclone by a particle counter-sizer-velocimeter. The results show that the size distribution upstream and downstream of the cyclone is almost a smooth curve. It could be used to calculate the total collection efficiency. The measured total efficiency by the particle counter-sizer-velocimeter is 2-3% higher than that measured by the weighing method. This close agreement between the two methods suggests that the total collection efficiency may be determined by the optical technique.