The microscopic dynamics of oxygen dissolved in liquid potassium is investigated by inelastic neutron scattering at a temperature of 550 K. Three oxygen concentrations in the melt were studied: 1.8, 5.1 and 8.5 at.%. A partial frequency spectrum of oxygen atomic vibrations and the frequency spectrum of potassium–oxygen melt are obtained from the analysis of double-differential scattering cross-sections. The average energy for oxygen noticeably exceeds the one for liquid potassium. The life time of oxygen atomic vibrations which is an order of magnitude less than that for potassium is estimated from the velocity autocorrelation function.