Sialylation of terminal glycoconjugates is involved in many important physiological and pathological processes such as tumor metastasis, drug resistance, organismal immunity, and viral infections. Sialyltransferases are enzymes responsible for sialylation modification in organisms, and potent sialyltransferase inhibitors can not only serve as probes for glycobiology studies, but also hold great promise to become agents for tumor therapy and viral infection control in the clinic. This review summarizes the latest progress in the development and application of various sialyltransferase inhibitors. The current challenges and development trends are also discussed.