Biomineralization is a highly efficient approach to synthesizing magnetic resonance imaging (MRI) probes but encounters two limitations: low metal loading and insufficient sensitivity. Herein, based on the Solomon-Bloembergen-Morgan theory and hard and soft acids and bases principle, we proposed the use of fully carboxylated albumin as a dual-purpose template for fabricating gadolinium oxide (BSA-COOH-Gd2O3) nanoprobe with high metal loading and exceptional relaxivity for the first time. The proposed nanoprobe was synthesized using a straightforward one-pot method under mild conditions, exhibiting excellent biocompatibility, good water solubility, high Gd content (6 %), and outstanding relaxivity (41.17 mM-1s−1). In vivo magnetic resonance angiography (MRA) demonstrated that the BSA-COOH-Gd2O3 nanoprobe (0.05 mmol Gd/kg, equivalent to half of the clinical dose) exhibited a sustained and significantly enhanced vascular enhancement effect for at least 2 h with exceptional resolution, enabling clear visualization of vessels as small as 0.3 mm at 3.0 T and 0.13 mm at 9.4 T. Both the severity and location of vascular narrowing can be accurately identified in a carotid artery stenosis model and the tumor can be sensitively detected in a tumor model via the nanoprobe-based MRI. Our study provides an upgraded biomineralization technique for synthesizing high-performance MRI nanoprobes for various applications.