  We study the contributions to the branching ratios of $B_{s(d)}\to \gamma
\gamma$ decay in the sequential fourth generation model (SM4). We find that the
theoretical values of the branching ratios, ${\rm
BR}(B_{s(d)}\to\gamma\gamma)$, including the contributions of $m_{t'}$ and the
new $4 \times 4$ CKM (CKM4) matrix factors, $|V^{*}_{t's}V_{t'b}|$ and
$|V^{*}_{t'd}V_{t'b}|$, are much different from the minimal standard model (SM)
predictions. The new physics effects, especially contributed from the CKM4
matrix factors, can provide more than one order enhancement to the SM
prediction. It is shown that the decay $B_{s(d)}\to \gamma \gamma$ can test the
new physics signals from SM4.
