To avoid the necessity of having a large number of correlations to predict the dynamic properties of poly-dispersed fluidized bed systems, a statistical approach has been adopted in the present paper to get an expression which can predict such property from a knowledge of similar property of the individual species that constitute such heterogeneous bed. In the present paper, the dynamic property means any property that is associated with, or dependent on a term ＇＇velocity＇＇, e.g., beginning elutriation velocity, u(be); free settling velocity, u(t); onset semifluidization velocity, u(osf); expanded bed height, L(e), etc. Based on 10,517 computations, embracing 5 different dynamic properties of liquid-solid fluidized bed systems and covering 13 different averaging formulae - similar to those, used to calculate average particle size for a poly-dispersed system - the following expression has been found to give the best fit: P=[1/SIGMA(x(i)/p(i)3)]1/3