  The $\eta \to \pi^0 \gamma \gamma$ decay was investigated by the SND detector
at VEPP-2M $e^+e^-$ collider in the reaction $e^+e^-\to\phi\to \eta\gamma$.
Here we present the results and some details of this study. We report an upper
limit (90% c.l.) $Br(\eta \to \pi^0 \gamma \gamma)<8.4\times 10^{-4}$ as our
final result. Our upper limit does not contradict the earlier measurement by
GAMS spectrometer. To facilitate future studies a rather detailed review of the
problem is also given.
