The multiple-channel reaction SiH3CH3 + OH -> products (R1) and the single-channel reaction SiH4 + OH -> SiH3 + H2O (R2) have been studied by the direct dynamics method at the QCISD(T)/6-31 1++G(3df,3pd)//BH&H-LYP/6-311G(d,p) level. The rate constants for those reactions are calculated by improved canonical variational transition state theory (ICVT) with small-curvature tunneling (SCT) contributions in a temperature range 200-3000 K. For reaction (RI), H-abstraction from the SiH3 group is the major channel. Since methyl substitution increases the reactivity of Si-H bond in silane, the rate constants of (RI) are larger than those of (R2) over the whole temperature region. (c) 2005 Elsevier B.V. All rights reserved.