A dual-level direct dynamic method is employed to study the reaction mechanism of hydroxyl radical with (CH3)(3)COOH and (CH3)(2)CHOOH. Eight hydrogen abstraction channels are found for title reactions. The energy paths are optimized at the BH&H-HLYP/6-311G(d,p) level, and the energy profiles are further refined by interpolated single-point energies method at the CCSD(T) and QCISD(T) theories. Rate coefficients for the reactions of the OH with (CH3)(3)COOH/(CH3)(2)CHOOH are computed by the canonical variational transition-state theory with the small-curvature tunneling correction between 200 and 2000 K. The Arrhenius expressions k(1) (T) = 1.49 x 10(-26) T-4.71 exp(1981.92/T) and k(2) (T) = 1.58 x 10(-2) T-3.32 exp(210.59/T) over 200-2000 K are obtained.