Development of a chelator-free and biocompatible platform for the facile construction of gadolinium3+ (Gd3+)-loaded nanoparticle based probes for in vivo magentic resonance imaging (MRI) is still challenging. Herein, biocompatible Gd3+-loading melanin dots (Gd-M-dots) have been easily prepared and have exhibited good loading efficiency for Gd3+, high stability, and higher T1 relaxivity compared to the commercial Gd-1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) agent. Furthermore, Gd-M-dots showed unique photoacoustic (PA) properties, and a high PA imaging signal could be observed in vivo 1 h after injection. Compared to the traditional Gd3+-loaded nanoparticles for single-modal MRI, Gd-M-dots can also be radiolabeled with 64Cu2+ for positron emission tomography. Overall, these attractive properties of Gd-M-dots render them a promising imaging agent for various biomedical applications.