  We report results on the decay $B^{-} \to D_{CP}K^{-}$ and its charge
conjugate using a data sample of 85.4 million $B\bar{B}$ pairs recorded at the
$\Upsilon(4S)$ resonance with the Belle detector at the KEKB asymmetric
$e^{+}e^{-}$ storage ring. Ratios of branching fractions of Cabibbo-suppressed
to Cabibbo-favored processes are determined to be ${\cal B}(B^- \to D^0
K^-)/{\cal B}(B^- \to D^0 \pi^-)= 0.077 \pm 0.005(stat) \pm 0.006(sys)$, ${\cal
B}(B^- \to D_1 K^-)/{\cal B}(B^- \to D_1 \pi^-) = 0.093 \pm 0.018(stat) \pm
0.008(sys)$ and ${\cal B}(B^- \to D_2 K^-)/{\cal B}(B^- \to D_2 \pi^-) = 0.108
\pm 0.019(stat) \pm 0.007(sys)$ where the indices 1 and 2 represent the CP=+1
and CP=$-$1 eigenstates of the $D^{0}-\bar{D^{0}}$ system, respectively. We
find the partial-rate charge asymmetries for $B^{-} \to D_{CP}K^{-}$ to be
${\cal{A}}_1 = 0.06 \pm 0.19(stat) \pm 0.04(sys)$ and ${\cal{A}}_2 = -0.19 \pm
0.17(stat) \pm 0.05(sys)$.
