Multifunctional nanocomposites integrating mesoporous and luminescence properties into a single entity are synthesized via a facile and effective approach. Oleic acid capped β-NaYF4:Ce(3+)/Tb(3+) nanoparticles (NPs) are transferred into aqueous solution by cetyltrimethylammonium bromide (CTAB) surfactants, and further encapsulated with uniform mesoporous silica shell followed by the surface modification with poly(ethylene glycol) (PEG), leading to the formation of water-dispersible and biocompatible core-shell structured β-NaYF4:Ce(3+)/Tb(3+)@mSiO2-PEG (denoted as NPs@mSiO2-PEG) nanospheres. The as-synthesized nanospheres show a typical mesoporous structure and a green emission under UV irradiation. Doxorubicin hydrochloride (DOX), a widely used anti-cancer drug, is used as a model drug to evaluate the loading and controlled release behaviors of the NPs@mSiO2-PEG in phosphoric acidic buffer solutions (PBS) at different pH values (pH = 7.4 and 5.0). The composite carriers provide a pH-sensitive drug release pattern and the drug releases faster under lower pH value. The endocytosis process of fluorescein isothiocyanate (FITC)-labelled nanospheres is characterized using flow cytometry and confocal laser scanning microscopy (CLSM) against A549 cells. The in vitro cytotoxic effect against A549 cells of the DOX-loaded carriers is investigated in detail. In addition, the extent of drug release can be monitored by the variation of photoluminescence (PL) intensity of β-NaYF4:Ce(3+)/Tb(3+). Considering the good biocompatibility and pH-dependent drug release pattern, such core-shell structured luminescent NPs@mSiO2-PEG nanospheres have potential applications in controlled drug delivery.