A polydisulfide MRI contrast agent was obtained by grafting diethylenetriaminepentaacetic (DTPA) to disulfide-containing poly(amido amine)s-graft-poly(ethylene glycol) (PEG) followed by Gd(iii) complexation. Self-assembly of the MRI contrast agent obtained occurs in aqueous solution forming nanosized micelles with PEG shells and ionic complex cores. The chemistry and structures of the MRI contrast agent and assembly were characterized using NMR, GPC and DLS. Thiol-induced degradation of the backbone and the assembly of the MRI contrast agent were investigated using GPC and DLS, respectively, and easy degradation was observed. Poly(BAC-AMPD)-g-PEG-g-Gd-DTPA also shows a low cytotoxicity and a high r1 value, so it is promising to provide better MRI imaging with fewer side effects.