Biomass conversion to produce liquid, gaseous, and solid fuels is an attractive technology to meet rising energy resource demands.  In the conversion of biomass, pyrolysis is used to reduce the volatile matter content and generate gases, bio-oils, tars and biochar.  The biochar may be used as a blending agent in coal-combustion systems.  The resulting combustion characteristics of these biochars is dependent on pyrolytic temperatures and both the biochars structural properties and entrained inorganic elements.  This study characterized the elemental and structural composition of biochars made from six biomass sources.  Each biomass was processed at two different pyrolysis temperatures and then examined for relationships between compositional properties and their thermochemical characteristics.  Biochars contained a variety of pH, ash contents, volatile matter and inorganic macro and micro-elements.  Higher pyrolysis temperatures resulted in aliphatic and carbohydrate losses and an enrichment of aromatic moieties.  When compared to their low temperature homologues, high temperature biochars were observed to have greater onset temperatures and an increase in a more uniform energy released per gram based on thermogravimetric combustion curves.