Nanoparticles with strong paramagnetic responses are of prime interest for advanced MRI imaging. To replace Gd expensive and toxic complexes, Gd-based nanoparticles have emerged as a viable solution for efficient and harmless MRI contrast agents. Gadolinium oxysulfide nanoparticles could represent suitable candidates for MRI imaging and bimodal imaging thanks to their excellent properties as host matrix and chemical stability, but their magnetic properties at the nanoscale have been hitherto poorly investigated especially in the case of ultrafine nanoparticles (< 10 nm), where surface effects and ligands can significantly affect the magnetic behavior. In the present work, we synthesized and characterized bimetallic (Gd,Ce) 2 O 2 S nanoparticles and demonstrated that they are paramagnetic over a wide 2 temperature range including the body one. The mixture of Gd and Ce magnetic centers enables a fine control of the magnetic properties up to high Ce concentrations (80 %) and over a large range of magnetic moments, while photoemission properties are guaranteed up to 20 % of Ce owing to a regular dispersion of the Ce centers. The present study on bimetallic oxysulfide nanoparticles with high concentrations of two lanthanides shows that (Gd,Ce) 2 O 2 S nanoparticles are viable candidates as tunable nanoscaled agents for bimodal imaging.