Magnesium chloride compound nanoparticles (MgCl₂ NPs) were chosen as alternative contrast medium in magnetic resonance imaging (MRI). The solution of MgCl₂ NPs was a good electrochemical property especially in the blood medium. It was found that MgCl₂ NPs in blood medium served as an antioxidant reagent because cyclic voltammogram had only one reduction current peak at 0.9 V. Gadolinium compounds were used as a common contrast medium in MRI technique; they had two oxidation current peaks in the blood medium at 0.73 V and 0.23 V. In addition, the gadolinium compounds caused many problems when used as a contrast medium, but they were the only contrast media used for this purpose. It was found that using MgCl₂ NPs solution as an alternative contrast medium in rabbits enhanced MR imaging of kidney organ, as compared with that using gadolinium at the same dose.