A systematic theoretical and experimental study was conducted to obtain hydrodynamic properties such as particle size diameter, bulk density, fluidizing velocity, etc. for locally available biomass residue fuels in Malaysia like rice husk, sawdust, peanut shell, coconut shell, palm fiber as well as coal and bottom ash. The tests were carried out in a cold flow fluidization bed chamber of internal diameter 60 mm with air as fluidizing medium. The height of the chamber could be raised up to 630 mm by five separate cylindrical rings. Bed-pressure drop was measured as a function of superficial air velocity over a range of bed heights for each individual type of particle. The data were used to determine minimum fluidization velocity, which could be used to compare With theoretical values. The particle size of biomass residue fuel was classified according to Gildart's distribution diagram; The results show that Gildart's particle size (B) for sawdust, coal bottom ash, coconut shell have good fluidizing properties compared to rice husk, type (D) or palm fiber, type (A). The bulk density and voidage are found to be main factors contributing to fluidizing quality of the bed. (C) 2003 Elsevier Science Ltd. All rights reserved.