Sulfur, like oxygen, belongs to group 16 of the periodic table and exhibits remarkable versatility in both electron donation and acceptance, as well as in its wide range of oxidation states. These properties enable sulfur to participate in diverse redox reactions, while also serving as a critical component of enzyme active sites and redox sensors. Moreover, sulfur is the only element capable of forming stable linear homonuclear chains, a property known as catenation, which gives rise to a rich array of naturally occurring allotropes with complex chemical architectures. Recent advances in analytical technologies have uncovered the in vivo existence of supersulfides, molecules containing catenated sulfur atoms, whose physiological functions and pathological relevance are now beginning to be elucidated. In this review, we highlight the unique chemical features and biological functions of supersulfur species, with a particular focus on their roles in cancer. Furthermore, we discuss the therapeutic implications of supersulfur-driven “reductive stress,” a distinct imbalance in redox homeostasis that may be exploited for cancer treatment.