  Let $g$ be a metric on hemisphere $S^{n}_{+}$ ($n\geq 3$) which is conformal
to the standard round metric $g_0$. Suppose its $Q$-curvature $Q_g$ is bounded
below by $Q_0$, we show that $g$ is isometric to $g_0$, provided that the
induced metric on $\partial S^{n}_{+}$ coincides with $g_0$ up to certain
order.
