Theranostic magnetic resonance imaging (MRI) is now receiving a growing interest in imaging-guided drug delivery, monitoring the treatment and personalized administration etc. Theranostic agents are essential for the usage of theranostic MRI. Among different kinds of theranostic agents, gadolinium loaded nanoparticles (GdNPs) are one of the most promising theranostic agents which are very promising in combination of diagnostics (molecular imaging) and therapeutics (molecular therapy) functions in a single platform. In this review, we provided fully discussion on the design considerations of GdNPs as a platform for theranostic MRI. The mainly factors that affect the preparation process, such as GdNP materials, the loading of Gd/drugs in GdNPs, and the passive and active targeting strategies were discussed. Major classes of GdNPs including lipid-based nanoparticles, polymeric nanoparticles, micelles, dendrimers and Gd-silica nanoparticles were described in detail. The use of GdNPs as theranostic agents offers potential advantages that change the usual cancer therapy from separating diagnosis and treatment to theranostic approach.