Purged pressure probes and a data reduction method by means of a rectangular pressure drop pulse (RPDP) have been developed to measure pierced bubble size and velocity for Group A powders using specially prepared size fractions of FCC powders in a 0.152 m fluidization column. Measurement results show that there exists an equilibrium bubble size of about 4 cm for FCC powders smaller than 70 mu m, and the measured bubble sizes are compared with the Geldart equation and Werther＇s correlation. The measurement results of bubble velocity show that bubble velocity can be correlated based on the Davidson and Harrison equation as: u(b) = u - u(mf) + 1.5 root gd(b).