  We construct supersymmetric (SUSY) grand unification (GUT) models in the six
dimensional space-time where the GUT symmetry is broken down to the
standard-model gauge group by a simple orbifolding T^2/Z_4 or T^2/Z_6 and a
pair of massless Higgs doublets in the SUSY standard model are naturally
obtained. Since the background geometry here is simple compared with models
using the Scherk-Schwarz mechanism, one might hope for an approximate gauge
coupling unification in the present models. Here, the presence of the massless
Higgs multiplets in the bulk is quite natural, since the anomaly cancellation
in the six dimensional space-time requires N=2 hyper multiplets in the bulk,
some of which are origins of the Higgs doublets. However, the origin of the
quarks and leptons is still not clear at all.
