Gadolinium (Gd)-based complexes are extensively utilized as contrast agents (CAs) in magnetic resonance imaging (MRI), yet, suffer from potential safety concerns and poor tumor targeting. Herein, as a mimic of Gd complex, single-atom Gd nanoprobes with r 1 and r 2 values of 34.2 and 80.1 mM -1 s -1 (far higher than that of commercial Gd CAs) at 3 T are constructed, which possessed T 1 /T 2 dual-mode MRI with excellent stability and good tumor targeting ability. Specifically, single-atom Gd is anchored on nitrogen-doped carbon matrix (Gd-N x C) through spatial-confinement method, which is further subjected to controllable chemical etching to afford fully etched bowl-shape Gd-N x C (feGd-N x C) with hydrophilic properties and defined coordination structure, similar to commercial Gd complex. Such nanostructures not only maximized the Gd 3+ site exposure, but also are suitable for self-confirmative diagnosis through one probe with dual-mode MRI. Moreover, the strong electron localization and interaction between Gd and N atoms afforded feGd-N x C excellent kinetic inertness and thermal stability (no significant Gd 3+ leaching is observed even incubated with Cu 2+ and Zn 2+ for two months), providing a creative design protocol for MRI CAs.