An approach was made to predict the minimum fluidization velocity for binary mixtures of spherical particles differing in size and/or density. The spherical multi-particle model proposed by Panigrahi and Murty was employed to describe the relationship between the bed pressure drop and the gas velocity; the voidage at minimum fluidization was estimated by the Westman equation, which was originally used to calculate the packing voidage of mixtures. The predictions agree fairly well with the reported experimental data in the range of Re = 0.12-156, covering both the regions of laminar flow and intermediate flow.