A hydrogen treatment followed by calcination, has been developed in order to enhance the intrinsic coercivity of Sr-hexaferrite (SrFe12O19). Fully hydrogen-treated Sr-hexaferrite consists of a mixture of 73%, by weight, of alpha Fe and 27% of Sr7Fe10O22 phases. Calcination of this material to reform the SrFe12O19 phase occurs in two stages. Between room temperature and 600 degrees C, oxygen was absorbed resulting in a large increase in weight with the formation of a mixture of SrFeO3-x, and Fe2O3 (alpha and gamma). During the second stage, the intermediate phases reacted to form SrFe12O19 at a temperature of between 700 and 800 degrees C. A partial desorption of oxygen occurred until calcination reached completion at 1000 degrees C. The magnetization at 1100 kA m(-1) and the remanence were similar to those of the untreated material, but, because of a much refined grain size, the intrinsic coercivity was considerably larger, with values around 400 kA m(-1). Grain growth occurs at temperatures >1000 degrees C, resulting in a decrease in the intrinsic coercivity.