To design functional nanomaterials for biomedical applications, the challenge for scientists is to gain further understanding of their unique toxicological properties. Nonspecific adhesion of proteins and endocytosis are considered to be the major biotoxic sources of imaging nanoprobes. Here, we fabricated ultrathin gadolinium oxide (Gd2O3) nanocoils with a low Young's modulus, which provides transformable properties in solution. The spatial configurational freedom of ultrathin nanocoils induces the steric repulsion to the nonspecific adsorption of proteins that, in turn, suppresses cellular uptake and thus improves their biocompatibility. The larger number of exposed surface gadolinium atoms of the ultrathin nanocoils provided enhanced T1 magnetic resonance (MR) imaging contrast with high signal activation. Such nanocontrast agents were applied to in vivo MR bioimaging to achieve prolonged circulation lifetime. The improved biocompatibility by transformable Gd2O3 nanocoils could open up a new perspective toward the design and construction of various nano-biomedicines in the future.