  We investigate a radiative correction to the masses of Kaluza-Klein(KK) modes
in a universal extra dimensional model which are defined on a six-dimensional
spacetime with extra space as a two-sphere orbifold $S^2/Z_2$. We first define
the Feynman rules which are necessary for the calculation. We then calculate
the one-loop diagrams which contribute to the radiative corrections to the KK
masses, and obtain one-loop corrections to masses for fermions, gauge bosons
and scalar bosons. We estimate the one-loop corrections to KK masses for the
first KK modes of standard model particles as a function of momentum cut-off
scale, and we determine the lightest KK particle which would be a promising
candidate of a dark matter.
