The initial stage of deoxidation and the influence of the oxygen level on the inclusion features were examined. Liquid Fe with various dissolved oxygen content (O) was brought into contact with Al in a quartz tube for a short time, i.e. 1, 5, 30 and 60 s. Microscopic investigations of the quenched samples revealed the formation of Al₂O₃ inclusions in the Fe–Al reaction zone, resulting from the motion of the diffusion front with time. Specific attention is given to inclusion size, location and morphology as a function of interaction time and O content. The latter was found to influence the inclusion characteristics. The inclusion number increased drastically with O content, which is related to the degree of supersaturation of the melt, one of the most important factors influencing the formation of inclusions. The inclusion morphology evolved from angular to spherical with increasing O content.