An experimental study on the segregation of fuel particles and of volatile matter during devolatilization in a fluidized-bed reactor is presented. The study was purposely carried out with beds of solids kept at incipient fluidization in order to focus attention on the segregation phenomena associated with the generation of endogenous bubbles. This term is used to denote bubbles of volatile matter formed around each fuel particle during devolatilization, as opposed to exogenous bubbles of fluidizing gas always present in aggregative fluidized beds. Experimental evidence of volatile bubble formation and of fuel particle as well as of volatile matter segregation is provided. Qualitative characterization of segregation patterns and quantitative assessment of the effect on segregation of variables like fuel particle size, density and volatile matter content, of bed solids size, of bed temperature are presented and discussed. Experimental data are further analyzed in the light of the theory developed in Part I (Fiorentino et al., 1996) in order to validate the model.