A non-intrusive method is presented to determine the residence times of a single particle in a facility composed of four interconnected fluidized beds (IFB) with glass beads fluidized by air above minimum fluidization at ambient temperature, It uses a glass particle labelled with radioactive Na-24 or Ir-192 whose gamma-ray emissions are monitored by two external NaI(Tl) scintillation detectors. It is shown that, within the batch particles’ size range, the mean residence time of the radiotracer particle is practically independent of the radiotracer particle size and the beds can be considered as practically ideally mixed vessels. It is further demonstrated that the method can adequately measure the residence time distribution of the particles independent of the processes occurring within the system such as the generation of static electricity during fluidization. The presence of static electricity was found to substantially affect the mean residence time of the solids. By relating the bed mass and the mean residence time of the radiotracer particle, the solids circulation rate within the IFB can be obtained.