For the past several years, our research has been directed towards the preparation of various monodisperse nanoparticles through solventless processes. (I) A general method, termed as a “wrap/bake/peel process”, was developed for nanostructural transformation. Depending on the heat treatment conditions, spindle shaped hollow nanocapsules of either hematite or magnetite were able to be produced. (II) Self-assembled uniform-sized ferrite nanocrystals embedded carbon nanosheets were synthesized simultaneously through a single heating procedure using metal-oleate complex as the precursor for both ferrite and carbon. As a demonstration of the ferrite/carbon nanocomposite as electrode material for Li-ion battery, electrochemical experiments were carried out in a coin type cell assembly. The nanocomposite electrodes exhibited large power capability with good cycling stability. (III) A transformation of hydrophobic iron oxide nanoparticles to hydrophilic and biocompatible maghemite nanocrystals by controlled heat treatment followed by dextran coating was reported. Through the process, highly crystalline bare maghemite nanoparticles with high magnetization were produced. In vivo MR imaging using these nanoparticles showed significant signal enhancement.