Abstract Use of a packed bed microreactor for the first stage hydrodeoxygenation (HDO) of pyrolysis oil was investigated. The effects of various processing conditions such as temperature, hydrogen partial pressure, and residence time on Extent of HDO, hydrogen consumption, and space-time-consumption were investigated using reduced sulfided NiMo/Al 2 O 3 catalyst. External and internal mass transfer resistances were examined in the microreactor. High hydrogen consumption along with small oxygen removal suggests that in hydrodeoxygenation of pyrolysis oil hydrogenation cannot be avoided. Reactor plugging at 543 K due to coke formation/polymerization shows that first stage HDO at a temperature below 543 K was required to convert highly reactive compounds so that second stage HDO at higher temperature can be conducted to remove oxygen completely. Hydrogen consumption and percent oxygen removed for this first stage HDO are comparable to literature values; however, it is found that in a microreactor these values are attainable at much lower pressure and residence time.