Zirconia nanoparticles doped with Eu 3+ , Tb 3+ and Gd 3+ ions have been synthesized following the benzyl alcohol route. The nano-particles were coated with N-hydroxydodecanamide and encapsu-lated in PLGA-b-PEG-COOH nanomicelles. The magnetic and fluorescent properties of these hybrid nanocarriers were investi-gated, proving them to be potential dual-imaging contrast agents. Increasing interest has been focused on the design of nano-materials suitable for use as non-invasive diagnostic tools for biomedical applications. In particular, the combination of optically active components with a contrast agent (CA) for magnetic resonance imaging (MRI) is an attractive way to develop multifunctional probes for biological imaging and recognition. 1 Although many classes of biocompatible organic–inorganic hybrid materials are potentially useful, many presently available formulations require potentially toxic elements, and indeed, clinical translation of nanotechnology will require nano-particles with the lowest possible likelihood of toxicity. 2 Because of its low toxicity, zirconia (ZrO 2) can be considered a potential host matrix for the design and fabrication of inno-vative nanomaterials. 3 Its doping with lanthanides has been reported and, in particular, Eu 3+ was the most used because of its interesting optical properties. 4 Moreover, Gd-doped zirconia was recently studied with the aim of controlling the phase and morphology of the nanocrystals. 5 A tetrakis-based complex of Tb 3+ ions for the doping of amorphous zirconia nanoparticles has been also reported. 6 The synthesis of lanthanide ion doped (Ln-doped) nanoparticles is a well-established method: several synthetic routes have been reported involving wet chemical synthesis such as the sol–gel process, precipitation and micro-emulsion-based methods followed by annealing at high temperature. 7 Post-synthesis functionalization of metal and metal oxide nanoparticles through coating of their surface with organic molecules allows the achievement of stable colloidal disper-sions. Moreover, surface functionalization procedures are aimed at obtaining compatibility between the inorganic phase and the medium where they are supposed to be applied. One of the most important requirements for nanoparticles to be exploited in medicine as diagnostic and therapeutic agents is to be biocompatible and stable in biological media (e.g., phos-phate buffer saline and serum). These requirements are well fullled by coating the nanoparticle surface with biocompatible and biodegradable polymers, and polyethylene glycol (PEG)-based polymers are the most common choice. 8 Another requirement for nano-therapeutic and diagnostic devices is the possibility to be targeted at specic biological sites. These features are usually achieved with polymers known to be non-toxic, i.e. GRAS (Generally Recognized As Safe) or FDA-approved. 9 As a matter of fact, the most investigated nanosized carrier devices are made up of non-toxic micellar amphiphilic polymers that consist of PEG and a low molecular weight hydrophobic core-forming block such as poly(lactic-co-glycolic)-acid (PLGA) or poly(lactic)acid (PLA). The hydrophobic core serves as a natural carrier environment for the inorganic nanoparticles, being suitable also for the inclusion of lipophilic drugs and/or metallic NPs at the same time. The hydrophilic shell allows the stabilization of the whole hybrid nanostructure in aqueous media. 10 Herein, we report the synthesis and the organic functional-ization of Ln-doped and co-doped zirconia nanoparticles, and their encapsulation in the PLGA-b-PEG-COOH nanomicelles