  We construct a supersymmetric standard model in the context of the Z_{12-I}
orbifold compactification of the E_8 x E_8' heterotic string theory. The gauge
group is SU(3)_c x SU(2)_L x U(1)_Y x U(1)^4 x [SO(10) x U(1)^3]' with
sin^2\theta_W = 3/8. We obtain three families of SO(10) spinor-like chiral
matter states, and Higgs doublets. All other extra states are exactly
vector-like under the standard model gauge symmetry. There are numerous
standard model singlets, many of which get VEVs such that only the standard
model gauge symmetry survives and desired Yukawa couplings can be generated at
lower energies. In particular, all vector-like exotic states achieve superheavy
masses and the R-parity can be preserved.
