A Powder-Particle Fluidized Bed (PPFB) is applied to the calcination of small limestone particles 2-64 mu m in mean diameter. The effects of reaction temperature, size of limestone particles, superficial gas, velocity, static bed height of medium particles, and inlet CO2 concentration upon the calcination conversion are investigated. Under conditions where the average residence time of gas in the bed is 0.4 s, more than 95% calcination is achieved in the case of 5 mu m limestone at temperatures higher than 1173 K, The dependence of calcination conversion on 20 vol% CO2 in fluidizing gas becomes small at temperatures higher than 1123 K.