Schlafen (SLFN) family genes were initially found in humans and rats to regulate cell growth and T cell differentiation, and exist widely in mice, horses, humans and other species and exhibit high homology. Lines of evidence suggest that SLFN proteins play important roles in inhibiting cell proliferation, promoting meiosis, regulating hematopoietic cells, reducing platelet numbers and the immune response, and also exert antiviral functions against several virus species including HIV-1, influenza virus and others. In addition, SLFN proteins have also been found to be closely related to cancer therapy, and act as a molecular marker to predict tumor development and the sensitivity to chemotherapy drugs. In this review, we discuss the classification, structures, characteristics, location and functions of SLFN family proteins, and focus on progress related to tumor and virus infection, aiming to provide new thoughts on exploration of SLFN protein functions and the underlying mechanisms.