Fine particles formed during pyrolysis are the precursors of particulate matters (PM) after combustion and/or gasification. This study aims to conduct a preliminary research on the characteristics of fine particles. The rapid pyrolysis of raw and acid-washed biomass was conducted in a drop tube furnace (DTF) with a wall temperature 1073-1473 K and varied residence times. Components of fine particles formed during rapid pyrolysis were determined by investigating their morphologies and element contents. Particle size distributions (PSDs) of fine particles were also measured by granulometry technique. The results showed that the yields of fine particles increased significantly with increasing pyrolysis temperature. PSDs of fine particles formed at different conditions varied from each other, and trimodally distribution was identified for fine particles derived from pyrolysis of raw biomass at 1473 K. Those independent fine particles consisted of abundant small fragments, and slight soot and ash particles. The size of soot and melting ash particles increased with residence time and temperature, and the size ranges of small fragments broadened as residence time increased.