  We study the vacuum structure in 5D SO(10) grand unified theory (GUT)
compactified on $S^1/Z_2$ orbifold, where SO(10) is broken into $SU(3)\times
SU(2)\times U(1)^2$ through the boundary conditions. Although a lot of people
extended to 6D to avoid massless colored particle, we can show they obtain
finite masses by the radiative corrections. In a supersymmetric case, the
fermionic partner of the zero-mode can also acquire non-vanishing mass through
the SUSY breaking effects, and the gauge coupling unification can be recovered
by use of brane localized kinetic terms.
