We propose a grand unified SU(5) x U(1)x model, where the standard SU(5) grand unified theory is supplemented by minimal seesaw and a right-handed neutrino dark matter with an introduction of a global Z(2)-parity. In the presence of three right-handed neutrinos (RHNs), the model is free from all gauge and mixed-gravitational anomalies. The SU(5) symmetry is broken into the Standard Model (SM) gauge group at MGUT similar or equal to 4 x 10(16) GeV in the standard manner, while the U(1)x symmetry breaking occurs at the TeV scale, which generates the TeV-scale mass of the U(1)x gauge boson (Z' boson) and the three Majorana RHNs. A unique Z(2)-odd RHN is stable and serves as the dark matter (DM) in the present Universe, while the remaining two RHNs work to generate the SM neutrino masses through the minimal seesaw. We investigate the Z'-portal RHN DM scenario in this model context. We find that the constraints from the DM relic abundance, and the Z' boson search at the Large Hadron Collider (LHC), and the perturbativity bound on the U(1)x gauge coupling are complementary to narrow down the allowed parameter region in the range of 3.0 <= m(z)'[TeV] <= 9.2 for the Z' boson mass. The allowed region for m(z)' <= 5 TeV will be fully covered by the future LHC experiments. We also briefly discuss the successful implementation of Baryogenesis and cosmological inflation scenarios in the present model. (C) 2018 The Authors. Published by Elsevier B.V.