In this work we report on the synthesis of two hydrophobic and degradable gadolinium poly(epsilon-caprolactone) conjugates and their use for the preparation of MRI-visible nanoparticles intended for diagnosis applications. Advantage has been taken from functional poly(epsilon-caprolactone)s (PCL) bearing propargyl (PCL-yne) or amine groups (P(CL-co-NH2VL)) to yield conjugates by following two strategies. In a first approach, an azido-chelate of gadolinium (Gd(III)) has been conjugated by CuAAC to PCL-yne to yield a polymeric chelate containing 2.6 wt% of Gd(III). In a second approach, a dianhydride Gd(III)-ligand was reacted with P(CL-co-NH2VL) to yield, after complexation with Gd(III) salts, a polymeric chelate containing 15.4 wt% of Gd(III). The polymers biocompatibility was assessed against L929 fibroblasts. In a second part, advantage was taken from the PCLs conjugates hydrophobicity to easily prepare by nano-precipitation nanoparticles with diameters ranging from 120 to 170 nm. The nanoparticles MRI-visibility was then evaluated and confirmed under the spin-echo and the clinically relevant gradient-echo MRI sequences. (C) 2014 Elsevier Ltd. All rights reserved.