  We study the color-allowed $\Lambda_b\rightarrow \Lambda_c \pi, \Lambda_cK$
decays in the perturbative QCD approach (PQCD) to lowest order in strong
coupling constant $\alpha_s$. Both the factorizable and nonfactorizable
contributions are taken into account in our calculations. It is found that
these processes are dominated by the factorizable contributions, while the
important nonfactorizable contributions can enhance the branching ratios by
about 30$\%$. The decay branching ratios are predicted to be
$\mathcal{B}(\Lambda_b\rightarrow \Lambda_c \pi)=6.7^{+4.1}_{-3.8}\times
10^{-3}$ and $\mathcal{B}(\Lambda_b\rightarrow \Lambda_c
K)=5.0^{+4.0}_{-3.0}\times 10^{-4}$, where the uncertainties arise from the
baryon light-cone distribution amplitudes (LCDAs), the heavy charm quark and
charmed baryon masses, and the hard scales. It is shown that the asymmetry
parameters in the two decays are approximately equal to -1, which is expected
as in the heavy quark limit and the soft meson limit. Our predictions are
consistent with the recent experimental data within errors. The obtained
numerical results are also compared to those in the other theoretical
approaches when they are available.
