Abstract: Investigations of the transition from bubbling to turbulent fluidization were conducted in a gas-solid fluidized bed using on-line computer analysis of pressure fluctuation. In order to study the effects of density and size of the particles as well as bed geometry on the transition, a series of experiments were performed. A correlation was obtained for the flow pattern transition velocity, U_C. Besides, it has been found that the Geldart’s classification of particles also predicts flow pattern transition.