CuInSe2 thin films have been prepared by selenizing Cu/In metal layers both at 450-degrees-C for 1 h and at 570-degrees-C for 10 min with pure selenium as a selenium vapour source. The H-2/N2 volume fraction was varied during the selenization and the effect of H-2 in the selenizing atmosphere on the properties of the CuInSe2 films was investigated by analysing the morphological, structural and compositional changes of the CuInSe2 films. All the selenized CuInSe2 thin films crystallized in a chalcopyrite structure and the grain size of the CuInSe2 films 1 mum thick ranged from 1 to 3 mum. The films had a more (112) preferred orientation and both the a axis and c axis lattice constants increased with increasing amount of hydrogen in the selenizing atmosphere up to 15 vol.%. Also, the resistivity and its activation energy increased significantly as the hydrogen volume percentage in the selenizing atmosphere increased. The compositional analysis showed that the Cu/In ratios decreased with increasing hydrogen volume percentage. The results indicated that the role of hydrogen in the selenizing atmosphere was to reduce the indium loss during selenization, causing increases in the (112) texture. the a axis and c axis lattice constants and the electrical resistivity.