In the present investigation the phase relations within the Ce–Al–Fe–S system have been clarified, using a combination of optical microscopy and WDS microprobe analyses. As a starting point high-purity charge materials of cerium, aluminium and FeS2 are melted and superheated to about 2000°C within small tantalum crucibles inside a dedicated laboratory furnace filled with cleaned argon. The phases detected in the as-solidified samples were CeS, Ce3Al, Fe2Ce and γ-Ce, along with Ce2O2S, which is an undesirable microconstituent in CeS-based grain refiners. It is concluded that FeS2 can be used as a sulphur source for addition up to about 4 wt% sulphur. At higher levels the Fe–Ta interaction becomes so vigorous that tantalum no longer acts as an inert refractory metal and wetting becomes a major problem. In contrast, aluminium is an essential alloying element in the sense that it prevents the grain refiners from disintegrating in contact with air due to internal oxidation of free cerium by promoting the formation of Ce3Al.