  Within the perturbative QCD approach, we re-calculate the branching ratio and
polarization fractions of the pure annihilation decay $B \to \phi \phi$ in both
the standard model (SM) and the family non-universal $Z^\prime$ model. We find
that this decay is dominated by the longitudinal part, while the transverse
parts are negligibly due to the absence of the $(S-P)(S+P)$-type operator. In
SM, the branching ratio is predicted as $(4.4^{+0.8+0.3}_{-0.6-0.5}) \times
10^{-8}$, which is larger than the previous predictions. With an additional
$Z^\prime$ boson, the branching ratio can be enhanced by a factor of 2, or
reduced one half in the allowed parameters space. These results will be tested
by the ongoing LHCb experiment and forthcoming Super-B experiments. Moreover,
if the $Z^\prime$ boson could be directly detected at hadron collider, this
decay can be used to constrain its mass and the couplings in turn.
