A simplified solution for the removal efficiency of a polydispersed aerosol by a cyclone collector is studied theoretically. The radial back mix approach based on Leith and Licht (1972) was modified and the moment method, which assumes the particle size distribution as a lognormal distribution, was used for numerical calculation. Consequently, the influence of polydispersity on overall collection efficiency was evaluated in a cyclone collector. The obtained simple and straightforward results give information on change of the particle size distribution such as total particle number concentration, geometric mean particle diameter, and geometric standard deviation through the cyclone collector. This obtained model also shows how the particles are collected throughout the cyclone as a function of time.