  We study the annihilating dark matter contribution to the extra-galactic
diffuse gamma-ray background spectrum, motivated by the recent observations of
cosmic-ray positron/electron anomalies. The observed diffuse gamma-ray flux
provides stringent constraint on dark matter models and we present upper bounds
on the annihilation cross section of the dark matter. It is found that for the
case of cored dark matter halo profile, the diffuse gamma-rays give more
stringent bound compared with gamma-rays from the Galactic center. The Fermi
satellite will make the bound stronger.
