  We study low-energy properties of spin-$S$ Kitaev models in an anisotropic
limit. The effective form of a local conserved quantity is derived in the
low-energy subspace. We find this is the same as that of $S=1/2$ case for the
half-integer spins but shows a different form for the integer spins. Applying
the perturbation theory to the anisotropic Kitaev model, we obtain the
effective Hamiltonian. In the integer spin case, the effective model is
equivalent to a free spin model under an uniform magnetic field, where quantum
fluctuations are quenched. On the other hand, in the half-integer case, the
system is described by the toric code Hamiltonian, where quantum fluctuations
play a crucial role in the ground state. The boundary effect in the anisotropic
Kitaev system is also discussed.
