  We study the four-body baryonic $B\to {\bf B_1 \bar B_2}M_1 M_2$ decays with
$\bf B_{1,2}$ ($M_{1,2}$) being charmless baryons (mesons). In accordance with
the recent LHCb observations, each decay is considered to proceed through the
$B\to M_1 M_2$ transition together with the production of a baryon pair. We
obtain that ${\cal B}(B^-\to \Lambda\bar p \pi^+\pi^-)=(3.7^{+1.5}_{-1.0}
)\times 10^{-6}$ and ${\cal B}(\bar B^0\to p\bar p \pi^+\pi^-,p\bar p \pi^+
K^-)=(3.0\pm 0.9,6.6\pm 2.4)\times 10^{-6}$, in agreement with the data. We
also predict ${\cal B}(B^-\to\Lambda\bar p K^+ K^-)=(3.0^{+1.3}_{-0.9})\times
10^{-6}$, which is accessible to the LHCb and BELLE experiments.
