Thymocyte selection-associated high mobility group box (TOX), a member of the high mobility group protein super-family, plays an important role in T cell development, functional maintenance, and exhaustion. It has been recently found that TOX exerts critical immunoregulatory functions during pathogen infections, and TOX expression is strongly associated with the intensity and tolerance of host immune responses. This review systematically summarizes the structural and functional features of TOX and focuses on its expression dynamics, mechanisms of action, and immunomodulatory effects during viral, bacterial, and parasitic infections, which provides a theoretical support to better understanding of the role of TOX in infectious diseases and provides new insights into development of potential immunotherapeutic strategies targeting TOX.