The development of free-cutting steel is inseparable from the development of environmentally friendly alloy elements and the control of inclusions shape. Alloying elements can affect the composition, morphology, size, and distribution of inclusion, which are the main factors affecting the machinability of free-cutting steel. This study selected sulfur free-cutting steel with different chemical compositions as the research object to examine the effects of bismuth and bismuth tellurium on sulfur-containing free-cutting steel through electrolytic corrosion experiments, metallographic microscopy, scanning electron microscopy, energy spectrum, and electron backscattering analyzer. The results showed that the microstructures of free-cutting-steel containing sulfur, free-cutting steel containing sulfur bismuth, and free-cutting steel containing sulfur bismuth tellurium are composed of ferrite, pearlite, and inclusions. The inclusions in sulfur-containing free-cutting steel are chain, cluster,