This paper presents the effects of molecular structure on the catalytic behavior of bio-oil components in the steam-re-forming reactions. Methanol, ethanol, I-propanol, butanol, 2-propanol, 1,2-propanediol, glycerol, propionaldehyde, acetone, and propionic acid were used as model compounds. Steam re-forming of the alcohols with a long carbon chain was relatively difficult and yielded large amounts of CH4 and coke deposits. An increased number of hydroxyl groups in the alcohols suppressed the generation of CH4 while promoting the production of CO and coke deposits. Furthermore, the location of the hydroxyl group also impacted both the product distribution and carbon deposition in the re-forming process. The type of functional group significantly affected steam re-forming as well. Alcohol steam re-forming tended to produce a significant amount of CH4, while aldehyde (propionaldehyde) steam re-forming produced only small amounts of CH4 and other organic byproducts. Severe coke deposition was encountered in the steam re-forming of ketone compounds such as acetone, since acetone showed a high tendency for polymerization to coke.