  We investigate the possibility that ultra-high energy cosmic rays (UHECRs)
originate from the annihilation of relic superheavy (SH) dark matter in the
Galactic halo. In order to fit the data on UHECRs, a cross section of
$<\sigma_Av>\sim 10^{-26}\textrm{cm}^2 (M_X/10^{12} \textrm{GeV})^{3/2}$ is
required if the SH dark matter follows a Navarro--Frenk--White (NFW) density
profile. This would require extremely large-$l$ contributions to the
annihilation cross section. An interesting finding of our calculation is that
the annihilation in sub-galactic clumps of dark matter dominates over the
annihilations in the smooth dark matter halo, thus implying much smaller values
of the cross section needed to explain the observed fluxes of UHECRs.
