Multifunctional hybrid materials are highly attractive in many applications, but in order to achieve these multifunctions it is essential to control the compatibility between nanoparticles (NPs) and the host polymer matrix. Synthesis of organically modified NPs in supercritical water has clear advantages over conventional functionalisation of NPs. Since the organic molecules and metal salt aqueous solutions are miscible in the supercritical domain, and the water molecule works as an acid/base catalyst for the reactions, organic-inorganic conjugate nanoparticles can be synthesised under supercritical conditions.