  Relic abundance of dark matter is investigated in the framework of universal
extra dimension (UED) models with right-handed neutrinos. These models are free
from the KK graviton problem in the minimal UED model. The first KK particle of
the right-handed neutrino is a dark matter candidate in this framework. When
ordinary neutrino masses are large enough such as the degenerate mass spectrum
case, the dark matter relic abundance can increase significantly. The scale of
the extra dimension consistent with cosmological observations can be 500 GeV in
the minimal setup of UED models with right-handed neutrinos.
