  We study the quasi-two-body decays $B\to P D^{\ast}_0(2400) \to P D\pi $ with
$P=(\pi, K, \eta, \eta^{\prime})$ in the perturbative QCD factorization
approach. The predicted branching fractions for the considered decays are in
the range of $10^{-9}$-$10^{-4}$. The strong Cabibbo-Kobayashi-Maskawa (CKM)
suppression factor $R_{CKM}\approx \lambda^4 (\bar{\rho}^2 + \bar{\eta}^2)
\approx 3\times 10^{-4}$ results in the great difference of the branching
ratios for the decays with $D_0^*$ and $\bar{D}_0^*$ as the intermediate
states. The ratio $R_{\bar{D}_0^{*0}}$ between the decays $B^0 \to
\bar{D}_0^{*0} K^0\to D^-\pi^+K^0$ and $B^0 \to \bar{D}_0^{*0}\pi^0 \to
D^-\pi^+\pi^0$ is about $0.091^{+0.003}_{-0.005}$, consistent with the
flavour-$SU$(3) symmetry result. The ratio for the branching fractions is found
to be $1.10^{+0.05}_{-0.02}$ between $\mathcal{B}(B_s^0\to D_0^{*+}K^-\to
D^0\pi^+K^-)$ and $\mathcal{B}(B^0\to D_0^{*+} \pi^-\to D^0\pi^+ \pi^-)$ and to
be $1.03^{+0.06}_{-0.07}$ between $\mathcal{B}(B_s^0\to\bar{D}_0^{*0}
\bar{K}^0\to D^-\pi^+ \bar{K}^0)$ and $2\mathcal{B}(B^0\to
\bar{D}_0^{*0}\pi^0\to D^-\pi^+\pi^0)$. The predictions in this work can be
tested by the future experiments.
