The electron paramagnetic resonance spectra of Cu2+ doped Na2HAsO4·TH2O single crystals were studied at room temperature. The results indicate the substitutional entrance of Cu2+ in two magnetically inequivalent Na+ sites. Charge compensation is supposed to be fulfilled by proton vacancies. The spin Hamiltonian parameters were determined. The ground state for Cu2+ seems to indicate the dominance of the dz2 orbital and therefore a compression of the distorted octahedron along its C4v axis.