The ability of superparamagnetic iron oxide nanoparticles (SPIONs) to shorten the effective transverse relaxation time (T₂) during magnetic resonance imaging (MRI) makes them excellent contrast agents in diagnostic applications. Here we describe a new class of hybrid MRI contrast agent using dispersions of lyotropic bicontinuous cubic phase nanoparticles doped with SPIONs. Hybrid mesophase nanoparticles (HMNs) combining the cubic order of a lyotropic lipid system and SPIONs were successfully prepared and characterized. Highly monodisperse 8 nm spherical SPIONs coated with oleic acid were dispersed in the bulk cubic phase forming lipid matrix of phytantriol nanoparticles 180 nm in size. Transverse relaxivity (r₂) measurements show that enhancement of the T₂ relaxation time of the HMNs is proportional to the loading of SPIONs in the mesophase nanoparticles. Excellent contrast enhancement in T₂ weighted images in the kidney and liver of live rats was observed after intravenous injection of the hybrid mesophase nanoparticles. Results indicate that the HMNs are rapidly transported to the renal system making them useful for contrast enhancement of renal and hepatic systems.