The production of ultra-fine solid particles with narrow size distribution requires creation of a very large, rapid, and uniform supersaturation in the solution of the solid substance. This is facilitated by a rapid, uniform, and large reduction of the solid solubility in the solution and can be achieved either by drastically reducing the temperature of solution or by drastically increasing the CO2 solubility for achieving the anti-solvent effect. As these processes have some disadvantages, a simple technique is reported in this work for imparting the large, uniform, and rapid reduction of temperature in the solution for the required supersaturation. This entails pressure reduction over the gas-expanded liquids utilizing subcritical CO2 at a relatively low pressure in the range of 40-70 bar and near ambient temperature of 303 K for creating a temperature drop of 30-70 K in the solution within seconds. The present article enunciates the principle of this new technique and analyses the effects of various process parameters on the reduction of temperature of the CO2-expanded organic solutions. (C) 2007 American institute of Chemical Engineers.