Local instantaneous temperature signals obtained in a two-story gas-solids circulating fluidized bed have been analyzed using chaos theory, Dominant frequencies were assessed using spectral analysis. The pseudo-phase space was used as a preliminary analysis for deterministic chaos in the experimental data. The correlation dimension was used to evaluate the fractal dimension, embedding dimension and the degree of freedom of the system. In respect to heat transfer process, two distinct regimes of particular fractal dimensions were identified: a dilute-particle-con trolled regime and a cluster-controlled regime.