  We deliver an exploratory lattice QCD examination of the $K^\ast(892)$ meson
decay width with the help of the p-wave scattering phase $\delta_1$ of
pion-kaon ($\pi K$) system in the isospin $I=1/2$ channel, which are extracted
by the modified Rummukainen-Gottlieb formula for two-particle system with
arbitrary mass, and it clearly reveals the entity of a resonance at a mass
around $K^\ast(892)$ meson mass. The effective range formula is applied to
describe the energy dependence of the scattering phase and we obtain the
effective $K^\ast \to \pi K$ coupling constant as $g_{K^\ast \pi K} =
6.38(78)$, and subsequently achieve the decay width to be $64.9 \pm 8.0$ MeV,
which is in reasonable accordance with the current experiment. Our lattice
investigations are conducted on a $20^3\times48$ MILC full QCD gauge
configuration at $(m_\pi + m_K) / m_{K^\ast} \approx 0.739$ and the lattice
spacing $a \approx 0.15$ fm.
