Biomass offers an alternative to meet the increasing interest in renewable energy. For thermal conversion processes such as fast pyrolysis, which often involve fluidization, spherical particles are considered unsuitable for materials such as biomass. An investigation was made of relevant physical properties of four types of biomass: sweet sorghum bagasse, tobacco waste, soybean hulls and fiber sorghum bagasse. Three samples of each biomass with different granulometries were analyzed. Density values were determined. Particle shape and size distributions were evaluated by digital image analysis. It was observed that the moisture content affected the materials' true density and for dried biomass the smaller the particle sizes the higher the true density. The results indicated that sweet sorghum bagasse particles of different sizes have similar shapes; that the particle roundness of the four types of biomass is a property more closely related with the characteristic shape of the material than with its granulometric classification; and that the granulometric classification of tobacco waste, soybean hull and fiber sorghum bagasse particles can effectively influence the obtainment of particles with higher or lower roundness. The average roundness varied from 0.45 to 0.70 and the aspect ratio from 1.90 to 2.60. The results obtained in this study are useful for numerical simulations of the fluid dynamics of plirolysis, combustion and gasification processes and also for studies about the optimal operating conditions of mixture fluidization. (C) 2013 Elsevier B.V. All rights reserved.