The many advantages of supercritical fluids come from their interesting or unusual properties which liquid solvents and gas carriers do not possess. The properties and possible applications of supercritical fluids are reviewed. As these fluids never condense at temperature above their critical temperatures, supercritical drying is useful to prepare a dry-gel. The solubility and other important parameters as a solvent can be continuously adjusted. The supercritical fluids show advantages as solvent for extractions, coatings or chemical reactions, due to these properties. Supercritical water shows a high solubility for organic matter and a strong hydrolyse ability. Supercritical water is expected to be useful in waste processings. Although they shows a high solubility for many solutes or molecular catalyses, solvent molecules under supercritical conditions gently solvate the solute molecules and have little influence on the activities of the solutes and the catalyses. This property would be attributed to the local density fluctuations around each molecule, due to the high molecular mobility. The fluctuations in the supercritical fluids would produce heterogeneity that would provide novel chemical reactions with molecular catalyses, heterogeneous solid catalyses, enzymes or solid adsorbents.

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