Fast pyrolysis of two biomass materials (mallee wood and pine wood) at 1300 degrees C was conducted in a novel drop tube furnace (DTF) with a double-tube configuration, which enables the direct determination of char yields. Three particle sizes (90-106, 150-250, and 250-355 mu m) were considered for investigating the effect of particle size on char yield, retention of alkali and alkaline earth metallic (AAEM) species, and shape of derived char particles from pyrolysis at such a high temperature. The experimental results show that the char yield increases with the biomass particle size and that the use of the ash tracer method with total ash, Mg, and Ca as a tracer can substantially overestimate the char yield by as high as 4.0% (absolute error) at actual char yields of mere similar to 1.0-3.4%. Additionally, a decrease in particle size significantly enhances the release of AAEM species during biomass pyrolysis. Such observations can at least be attributed to the considerably higher heating rate experienced by small particles during rapid pyrolysis, which is estimated to be 5.4 times of that experienced by large particles. For mallee wood, rapid pyrolysis of small biomass particles (90-106 mu m) forms nearly spherical char particles, while that of large biomass particles (250-355 mu m) tends to retain their elongated shape. This is due to extensive melting of small particles during rapid pyrolysis at 1300 degrees C, while large biomass particles only experience partial melting. For pine wood, particle size has no obvious effect on particle shape of pine chars that are mainly cenospheres with smooth surfaces, demonstrating severe melting of the cell structure.