Fluidized bed reactors behave as a continuously stirred tank reactor having wide residence time of solids, which is not desirable if a homogeneous product is required. The multi-stage fluidized bed reactors narrow the solids residence time, making it useful for various operations. A three-stage fluidized reactor was designed, fabricated and operated under stable operating condition to investigate the mean particle residence time in the system. The materials taken for the study were lime and sand. In the particle residence time experiments, the results revealed that at a particular solids velocity, mean residence time decreased with increase in gas velocity and increased with decrease in gas velocity. Based on the data, a correlation has been presented for predicting mean residence time.