In this study, we report an anticancer drug delivery system based on doxorubicin (DOX)-conjugated NaYF4:Yb3þ/Tm3þ nanoparticles. The as-synthesized nanoparticles consist of uniform spherical nanoparticles with an average diameter of 25 nm. The drug delivery system demonstrates the ability to release DOX by cleavage of the hydrazone bond in mildly acidic environments. The spectra overlap between emission of donor NaYF4:Yb3þ/Tm3þ nanoparticles at 452 nm (1 D2/3 F4) and 477 nm ( 1 G4/3 H6) and the broad absorbance of acceptor DOX centered at around 480 nm enables energy transfer to occur between the nanoparticles and DOX. The quenching and recovery of the up-conversion luminescence of NaYF4:Yb3þ/Tm3þ by DOX due to luminescence resonance energy transfer (LRET) mechanism are applied as optical probe to confirm the DOX conjunction and monitor the release of DOX. The DOX-conjugated NaYF4:Yb3þ/Tm3þ nanoparticles exhibit an obvious cytotoxic effect on SKOV3 ovarian cancer cells via MTT assay. Meanwhile, the endocytosis process of DOX-conjugated NaYF4:Yb3þ/ Tm3þ nanoparticles by SKVO3 cells was demonstrated through confocal laser scanning microscopy (CLSM), flow cytometry and ICP-OES. Such drug delivery system, which combines pH-triggered drugrelease and up-converting nanoparticles-based LRET property, has excellent potential applications in cancer therapy and smart imaging.