A comprehensive theoretical analysis is provided to demonstrate that the idea of the recycling of outlet gas of a cyclone as a means of improving its dedusting efficiency may be misleading. When the effects of particle size and solids loading are incorporated in the saltation velocity equation, it is predicted that the overall dedusting efficiency will be reduced if such a gas recycling system is adopted. It is also shown that the traditional equation for dedusting efficiency involving the cut size of particles may become invalid once the saltation velocity of the cut size exceeds the corresponding inlet gas velocity.