A new method to classify aerosol particles according to their mass-to-charge ratio is proposed. This method works by balancing the electrostatic and centrifugal forces which act on particles introduced into a thin annular space formed between rotating cylindrical electrodes. Particles having a mass-to-charge ratio lying in a certain narrow range are taken out continuously as an aerosol suspension. A theoretical framework has been developed to calculate the transfer function which is defined as the ratio of the exiting particle dux to the entering particle flux. A similarity rule has been derived which states that a single nondimensional constant determines the shape of the transfer function. To examine the feasibility of the proposed principle, a prototype classifier was constructed, and the mass distribution of monodisperse particles nominally 0.309 mu m in diameter was measured. The peak structures corresponding to singly, doubly,and triply charged particles were identified in the experimental spectra. The difference between theory and experiment in the peak location for the singly charged particles was about 6.5% in terms of mass, or 2.3% in terms of diameter.