The dispersion curves for spin waves propagating along the [0, 0, ζ], [ζ, ζ, ζ, 0], [ζ, ζ, ζ], [–ζ, –ζ, 2ζ], and [ζ, ζ, 1.5–2ζ] directions in MnCO3 at 4.6 °K have been determined by neutron inelastic scattering. The maximum spin-wave frequency is 0.95 ± 0.02 THz. Theoretical expressions for the spin-wave frequencies in MnCO3 are developed, and the interatomic exchange interactions determined by least-squares analysis. The dominant exchange interaction is the nearest-neighbor intersublattice interaction, J1 = −0.0290 ± 0.0011 THz. The next-nearest-neighbor intersublattice interaction, J2 = −0.0029 ± 0.0004 THz, and the nearest-neighbor intrasublattice interaction, [Formula: see text], are almost an order of magnitude smaller, and other interactions are negligible within experimental error.