In this work, the catalytic effect of titanium dioxide (TiO 2 ) on the online fast pyrolysis of cellulose was inves- tigated using a tandem micro reactor coupled to a gas chromatograph-mass spectrometer (GC -MS) system. This system was used in the following two different modes: in -situ and ex -situ . The results obtained with TiO 2 were compared with those of zeolite (HZSM-5) under identical pyrolysis conditions. Levoglucosan was the major product in the non -catalytic pyrolysis of cellulose. As for the catalytic pyrolysis of cellulose at 500 ? C with TiO 2 ( in -situ ), the peak of levoglucosan disappeared whereas aromatic hydrocarbons such as benzene, toluene and naphthalene were newly detected. In this case, oxygenated compounds such as furfural, furan, methylfuran were still observed for TiO 2 whereas oxygenated compounds (i.e, furan, benzofuran, methylbenzofuran, acetone and 2-butanone) with low yields were observed for in -situ catalytic pyrolysis with HZSM-5. For ex -situ catalytic py- rolysis of cellulose at 500 ? C using TiO 2 , oxygen -containing compounds were hardly formed, while various ar- omatic hydrocarbons were detected. When the ex -situ pyrolysis of cellulose with HZSM-5 was carried out, the yields of the aromatic hydrocarbons were comparable to those with TiO 2 .