We have proposed and developed a method of supercritical hydrothermal synthesis of metal oxide nanoparticles. Recently, we modified this new method to synthesize organic-inorganicbio-molecule fused materials. By introducing organic species (aminoacids, carboxylic acids, amines, alcohols, aldehydes etc.) during supercritical hydrothermal synthesis, nanoparticles whose surface was modified with organic materials were synthesized, which was probably due to the homogeneous phase formation in supercritical conditions. We succeed in synthesizing surface modified metal oxide nanoparticles (several to 20 nm), which cannot be synthesized by the other methods. Modification of bio-materials including amino acids or peptides is also pobible. This type of surface modification allows the designer to incorporate unique characteristics of the nanoparticles into their products, including perfect dispersion of inorganic nanoparticles in aqueous solutions, organic solvents or in polymers. This can be used for nanohybrid polymers, nano-ink, or nano-paints. Furthermore, biomodification of nanoparticles leads to form nanobiohybrid materials.