Mercury's core structure is crucial for understanding the planet's formation and evolution. Geodetic data from spacecraft missions and experimental simulations have shown that Mercury's core is enriched in light elements. The dominant light element is likely silicon (Si) which dissolves in metallic alloy under reduced conditions relevant to Mercury's core. Sulfur (S) likely also contributes to core formation. At the pressure of Mercury's core-mantle boundary (~6 GPa), if the sulfur content is high enough, a miscibility gap will form in the Fe-Si-S system, leading to the coexistence of two Fe-rich melts: a FeS-dominated sulfide melt and an FeSi metallic melt. Due to differences in interfacial tension between the S-rich and Si-rich melts and for stable density distribution, the S-rich melt preferentially wets the silicates and occupies the outer position. Geodetic analysis leaves the possibility for the presence of a liquid FeS outer core, while geochemical modeling indicates that the likelihood and thickness of such a layer is relatively low. Assuming enstatite chondrites (EHs) as building blocks, Mercury's core is thought to contain multiple light elements (e.g., carbon), which significantly influence the extent of the miscibility gap. The existence of an FeS layer is therefore highly dependent on the immiscibility extent in the Fe-Si-S±C system and the bulk sulfur concentration in Mercury's core. However, the behavior and interactions of these elements in the multicomponent system are not well understood, leading to uncertainties in constraining the core's structure. Here, we present a series of high-pressure and high-temperature experiments to explore the liquid immiscibility of the Fe-Si-S±C system under conditions relevant to Mercury's core. These results, combined with the bulk Mercury composition and sulfur solubility in silicate melts, will help calculate the bulk sulfur content of Mercury's core and provide valuable insights into the potential existence of an FeS outer core.