  A spin-1 Z' particle as a single dark matter candidate is investigated by
assuming that it does not directly couple to the Higgs boson and standard model
fermions and does not mix with the photon and Z boson. The remaining dominant
vertices are quartic Z'Z'ZZ and Z'Z'W+W-, which can induce effective
Z'Z'q\bar{q} couplings through standard-model gauge-boson loops. We discuss
constraints from the cosmological thermal relic density, and direct and
indirect-detection experiments, and find that a dark Z' can only exist above
the W boson mass threshold, and the effective quartic coupling of Z'Z'VV is
bounded in the region of 10^{-3}~10^{-2}.
