Oligosiloxanes having different distributions of Si-H groups were prepared, and the addition of Si-H bonds to C C double bounds of trimethyl(2-propenyloxy)silane was utilized to obtain oligosiloxanes having different distributions of gamma-trimethylsiloxy-propyl or gamma-hydroxy-propyl groups as substituents. The oligosiloxanes were characterized by IR and H-1-NMR spectroscopy. Viscosity was studied to investigate the effects of the substituents. Differential scanning calorimetry (DSC) was used to investigate the thermal behaviour of these oligosiloxanes. It was found that they are completely amorphous materials and, hence, show only a glass transition. We found that the viscosities and glass transition temperatures of these materials increased with the increasing of the number of substituents. Hydrogen bonds have a considerable influence on the increase of the viscosities and glass transition temperatures of oligosiloxanes.