The epr spectrum of Mn²⁺ has been studied in single crystals of BaO at X and Q band frequencies. This spectrum is distinctly different from the spectra of Mn²⁺ in other alkaline earth oxides. In BaO the Mn²⁺ ion occupies a site with a (111) axis of symmetry, the spectrum fitting the spin Hamiltonian H_s= beta B.g.S+SDS+IAS with g/sub ///=2.0017, g_{perpendicular to}=2.0013, D=0,0778 cm^-1, E<0.005 cm^-1, A/sub ///=67.5*10^-4 cm^-1 and A_{perpendicular to}=68.5*10^-4 cm^-1.