The isotope effects on the bifurcating reaction path of the isomerization reaction, H3CO -->H2COH (stereoisomers of P and P*), have been investigated recently [J. Chem. Phys. 113, 477 (2000)], and it was found that the valley-ridge inflection point appears in the totally symmetric direction relative to the intrinsic reaction coordinate in the deuterium-substituted system. In the present report, the kinetic isotope effect on this reaction has been studied using an ab initio direct-trajectory method at the computational level of the complete active space self-consistent field method with 6-31G(d,p) basis sets. The branching ratio to the respective stereoisomers has been investigated in terms of distributions of several coordinates along the trajectories. The energy landscape for H3CO is also described in terms of several structures and the respective permutational isomers.