AbstractNovel nanogels, characterized by high stability and incorporating macrocyclic chelates of Gd(III) and Dy(III), were synthesized and assessed for their effectiveness as T₁ and T₂ relaxation agents, respectively. In this specific design, we employed octacoordinated bifunctional Gd‐1,7‐DOTAGA₂ chelate to cross‐link chitosan chains. The results revealed that the sample exhibited a relaxivity value at clinical magnetic field strengths (1.5 T), approximately seven times higher than that of currently available clinical contrast agents and good MRI contrast efficacy at both 7.1 and 1 T. Furthermore, the nanogel displayed excellent stability in biological fluids, with no discernible interactions with serum biomolecules and no release of metal. In addition to Gd(III)‐based probes commonly used as T₁ positive contrast agents, the nanogel with the corresponding Dy‐1,7‐DOTAGA₂ chelate was prepared to explore its potential as a T₂ MRI probe. Dy‐based nanogel demonstrated notably elevated transverse relaxivity values compared to the free chelate at high magnetic fields (>3 T) and significant T₂ MRI contrast at 7.1 T, a capability often lacking when employing an equivalent concentration of a low‐molecular‐weight Dy(III) complex. The characterization of paramagnetic complexes was completed through the measurement of ¹H NMRD profiles and ¹⁷O NMR data.