  Gauge unification in a five dimensional supersymmetric SO(10) model
compactified on an orbifold $S^1/(Z_2 \times Z_2^{\prime})$ is studied. One
orbifolding reduces N=2 supersymmetry to N=1, and the other breaks SO(10) to
the Pati-Salam gauge group $\ps$. Further breaking to the standard model gauge
group is made through the Higgs mechanism on one of the branes. The differences
of the three gauge couplings run logarithmically even in five dimensions and we
can keep the predictability for unification as in four dimensional gauge
theories. We obtain an excellent prediction for gauge coupling unification with
a cutoff scale $M_* \sim 3 \times 10^{17}$ GeV and a compactification scale
$M_c \sim 1.5 \times 10^{14}$ GeV. Finally, although proton decay due to
dimension 5 operators may be completely eliminated, the proton decay rate in
these models is sensitive to the placement of matter multiplets in the 5th
dimension, as well as to the unknown physics above the cutoff scale.
