A new type of BaGdF(5):Yb/Er nanoprobe for dual-modal fluorescent and magnetic resonance imaging (MRI) is demonstrated. Water soluble and amine-functionalized BaGdF(5):Yb/Er nanoparticles (NPs) with average size of about 10 nm were synthesized by a facile one-pot hydrothermal method. The in vitro up-converted emission of BaGdF(5):Yb/Er NPs is observed in HeLa cells with near-infrared excitation at 980 nm and served as a fluorescent label. In addition, the cytotoxicity assay in HeLa cells shows low cell toxicity of the amine-functionalized BaGdF(5):Yb/Er NPs. Moreover, these BaGdF(5) NPs exhibit excellent intrinsic paramagnetic properties and enhanced T(1)-weighted MRI images with increased concentrations of BaGdF(5) NPs. Therefore, these results suggest that the amine-functionalized BaGdF(5) NPs with an optimized size and low cell toxicity are promising dual-modal bioprobes for optical bioimaging and MRI.