  We study the angular distributions of the baryon-antibaryon low-mass
enhancements in the three-body baryonic B decays of $B\to p\bar{p}M$ (M=K and
$\pi$) in the framework of the perturbative QCD. By writing the most general
forms for the transition form factors of $B\to p\bar{p}$, we find that the
angular distribution asymmetry in $B^-\to p\bar{p}K^-$ measured by the Belle
Collaboration can be explained. We give a quantitative description on the
Dalitz plot asymmetry in $B^-\to p\bar{p}K^-$ shown by the BaBar Collaboration
and demonstrate that it is equivalent to the angular asymmetry. In addition, we
present our results on $\bar B^0\to p\bar{p}K_S$ and $B^-\to p\bar{p}\pi^-$ and
we obtain that their angular asymmetries are $-0.35\pm0.11$ and $0.45\pm0.10$,
respectively, which can be tested by the ongoing experiments at the B
factories.
