Abstract: Upconversion nanoparticles (UCNPs) have many excellent chemical and optical properties such as high photostability, tunable luminescence and low biological toxicity, which have been widely used in the field of biological diagnosis and therapy. This review focused on the latest research progress of the application of UCNPs in biological diagnosis and therapy in the past 5 years, and outlined the applications of UCNPs in the fields of biological diagnosis, drug delivery, phototherapy, etc., providing guidance for future research and application of UCNPs in biological diagnosis and therapy.