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As one of main biomass wastes in Japan, Sugi (Japanese cedar) leaves were chipped and treated for preparation of charcoal at mild temperature (250 – 450 °C) using superheated steam with controllable pressure. After the treatment, the solid residual charcoal was examined by FT-IR and CHN elemental analysis. The results suggest that degree of carbonization was significantly affected by treating temperature, time and partial pressure of steam. A temperature above 400 °C and a partial pressure of steam above 4 MPa are necessary for accelerating and completing the carbonization within 2 hours. Adsorption experimental results of charcoal show that the residual charcoal has an excellent absorbability for ammonia gas and heavy metal ion Pb2+. Therefore it is expectable to develop mild superheated steam as reaction medium for preparing valuable charcoal products from biomass wastes with lower energy cost. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]