The upgrading of a fast pyrolysis bio-oil was studied with different catalysts in a fixed bed micro-reactor. The catalysts were HZSM-5 (average pore size, 0.54 nm), H-Y (0.74 nm), H-mordenite (0.67 nm), silicalite (0.54 nm) and silica-alumina (3.15 nm). The experiments were carried out at atmospheric pressure, 1.8 and 3.6 weight hourly space velocity, and a temperature range of 290-410 degrees C. The products were char, coke, gas, tar, residue, water and an organic distillate fraction (ODF). The objective was to obtain high yields of hydrocarbons in the ODF. The yields of hydrocarbons (based on the amount of bio-oil fed) were 27.9 wt% with HZSM-5, 14.1 wt% with H-Y, 4.4 wt% with H-mordenite, 5 wt% with silicalite and 13.2 wt% with silica-alumina. It was interesting to note that whereas HZSM-5 and H-mordenite produced more aromatic than aliphatic hydrocarbons, H-Y, silicalite and silica-alumina produced more aliphatic than aromatic hydrocarbons. The main aromatic hydrocarbons were toluene, xylenes and trimethylbenzenes. The liquid aliphatic hydrocarbon content consisted mostly of C6C9 hydrocarbons. Alkylated cyclopentene, cyclopropane, pentane and hexene were the main aliphatic hydrocarbons. In most of the runs, doubling the space velocity from 1.8 to 3.6 h-l resulted in decreased coke, char and gas formation and increased ODF yields. On the other hand, deoxygenation and hydrocarbon formation decreased.