Abstract: Dihydrofolate reductase (DHFR) is a well-known key target in the treatment of tumors, bacterial infections, and parasitic infections; and it plays a critical role in the biosynthesis of cellular DNA. DHFR inhibitors interfere with one-carbon metabolism by inhibiting substrate binding to DHFR, thereby inhibiting cell proliferation. Research on DHFR inhibitors has continued since the 1940s. To date, a variety of DHFR inhibitors have come into the market, primarily used for anti-tumor, antibacterial, antiparasitic, and anti-inflammatory therapy. This review summarizes the research progress of DHFR inhibitors with antitumor or antibacterial effects in recent years based on the classification of single-target and dual-target and looks forward to the opportunities and challenges faced by the work in this field.