  We consider decaying dark matter with masses $10^{7} \lesssim M \lesssim
10^{16}$ GeV, as a source of ultra-high energy (UHE) gamma rays. Using recent
limits on UHE gamma-ray flux for energies $E_\gamma > 2 \cdot 10^{14}$ eV,
provided by extensive air shower observatories, we put limits on masses and
lifetimes of the dark matter. We also discuss possible dark matter decay origin
of tentative 100 PeV photon flux detected with EAS-MSU experiment.
