  We study three-body charmless baryonic B decays of $B \to \Lambda\bar\Lambda
P$ with $P=\pi$ and $K$ in the standard model. We find that the branching
ratios of the $K$ modes are about one order of magnitude larger than those of
the corresponding $\pi$ modes unlike the cases of $B\to p\bar p P$. Explicitly,
we obtain that $Br(B^-\to \Lambda\bar \Lambda K^-)=(2.8\pm 0.2)\times 10^{-6}$
and $Br(\bar B^0 \to\Lambda\bar \Lambda \bar K^0)=(2.5\pm 0.3)\times 10^{-6}$.
The former agrees well with the BELLE experimental measurement of
$(2.91^{+0.90}_{-0.70}\pm 0.38)\times 10^{-6}$, while the latter should be seen
at the ongoing B factories soon.
