We propose a simple supersymmetric SO(10) GUT model with only doublet Higgs scalars. The fermion mass problem is naturally solved by a new one-loop diagram. R-parity is conserved implying a stable LSP which can explain the dark matter of the universe. There are two contributions to the neutrino masses, one of which depends on the quark mass squared while the other is independent and similar to the type II see-saw mechanism. In the latter case b − τ unification implies large neutrino mixing angles. The baryon asymmetry of the universe is explained through leptogenesis.The supersymmetric grand unified theories (GUTs) turned out to be the most natural extension of the standard model, in which all the gauge interactions unify to a single interaction. The simplest supersymmetric GUT with the gauge group SU (5) suffers from several problems like proton decay, unification of coupling constants, fermion masses and mixings. There are solutions to these problems, but each of these solutions makes the theory more complex. The most natural choice for the simplest GUT then turns out to be the one based on the group SO(10). All fermions, including the right-handed neutrinos belong to the 16-dimensional spinor representation of the group. At higher energies the theory predicts parity invariance and the generators of the group include leftright symmetry and B − L symmetry [1], which makes the theory even more attractive. As a consequence of the spontaneous breaking of the B − L symmetry, the neutrino mass comes out to be small naturally via the see-saw mechanism [2].There are many versions of the supersymmetric SO(10) GUT with varying predictions. The most popular version of the theory includes triplet Higgs scalars to break the left-right symmetry and simultaneously give Majorana masses to neutrinos. These triplets belong to a 126-dimensional representation and a 126-plet representation is required for anomaly cancellation. Recently a minimal SO(10) GUT has been proposed [3,4,5,6], in which the 126 explains light neutrino masses and mixing [4], solves the problem of wrong prediction for fermion masses in the SO(10) GUT [3], namely, m µ = m s and m e = m d , and conserves R-parity at low energies [5] implying a stable LSP which then solves the dark matter problem.In the present article we propose yet another simpler supersymmetric SO(10) GUT with only doublet Higgs scalars. Models with doublet Higgs scalars have been discussed in the past [7,8], but here we present a minimal model with doublet Higgs scalar, which has many advantages. The 126 and 126 of Higgs scalars are now replaced by 16 and 16 of Higgs scalars and one SO(10) singlet fermion per generation. This model has three more coupling constants, but has 217 less superfields compared to the minimal models with triplet Higgs scalars [6]. In addition, this model can be motivated by string theory, in which case the coupling constants will be determined by the string tension. This model can also be embedded in orbifold SO(10) GUTs naturally [8]. Leptogenesis is also possible...