The reaction of atomic O(P-3) with CH3CHCl2 has been studied theoretically using ab initio direct dynamics methods for the first time. This reaction involves two channels: H abstraction from the methyl group (CH3), and H abstraction from the methyne group (CH). Two nearly degenerate saddle points of (3)A(") and (3)A(') symmetries have been located for each hydrogen abstraction channel. At the QCISD(T)/6-311+G(3df,2p)//MP2/6-311G(d,p) level, the potential barrier of H abstraction from the CH3 group is higher about 6 kcal/mol than that of H abstraction from the CH group. Changes of geometries, generalized normal-mode vibrational frequencies, and potential energies along the reaction paths for all the channels are discussed and compared. On the basis of the ab initio data, the rate constants of each channel have been deduced by canonical variational transition state theory with small-curvature tunneling correction method over a wide temperatures range of 200-3000 K. The theoretical results have been compared with available experimental data. The kinetics calculations show that the variational effect is small and in the low temperature range (200-800 K), the small curvature tunneling contribution is important for all the channels. The detailed branching ratios have been discussed. (C) 2003 American Institute of Physics.