An in situ CVD method was developed in order to grow CNFs on Ni/alumina and nickel thin film catalyst coated inside a closed channel fused silica microreactor. By directly flowing reactant gases over a catalytic coating inside the microchannels, a mechanically stable and porous CNF-alumina composite was formed with high surface area (160 m(2)/g). Effects of growth time, growth temperature and H(2) addition during pretreatment and deposition steps on the composite thickness and nanofibers diameter were investigated. Hydrogen addition increases the deposition rate and helps in producing a mechanically stable support in the microchannel. (C) 2009 Elsevier B.V. All rights reserved.