The present invention relates to a paramagnetic polynuclear metal complex having enhanced self-relaxation rate and thermodynamic stability, and more particularly, to a synthetic method of a novel DTPA-bis-amide-histidine ligand and DTPA-bis-amide-aspartic acid ligand, a novel gadolinium complex ([Gd(L)H2O]) using the ligand, and a paramagnetic polynuclear metal complex using the gadolinium complex. The paramagnetic polynuclear metal complex is able to fix three or more metals (one gadolinium and two metal ions), thereby providing more excellent self-relaxation rate than the commercially available contrast agents. Thus, it can be widely applied to an MRI contrast agent because of meeting the high self-relaxation rate required as a contrast agent of magnetic resonance imaging (MRI).