A supercritical fluid process, called aerosol solvent extraction system(ASES), is especially suitable to the pharmaceutical, cosmetic and food industries due to its environmentally-friendly, non-toxic and residual solvent-free properties. In particular, the application of the ASES process to the processing of thermo-labile bioactive compounds has received attention of many scientists and engineers because of its low-temperature operating conditions. Unstable substances such as Vitamin-C and Vitamin-A can be effectively protected from degradation during the preparation process, because the ASES process is free from oxygen and moisture. In this study, Vitamin-C was formulated with 2-hydroxypropyl-${eta}$-cyclodextrin (HP-${eta$-CD) for enhancement of Vitamin-C stability and bioavailability using the ASES process. To investigate the influence of the preparation process on the stability of Vitamin-C, Vitamin-C/HP-${eta}$-CD inclusion complexes were prepared using both conventional solvent evaporation method and ASES process, and stored in a 50 mM phosphate buffer solution of pH 7.0 at $25^{circ}C$ for 24 hours. From the experimental results, the stability of the Vitamin-C/HP-${eta}$-CD inclusion complex prepared from the ASES process was found to be much higher than that of pure Vitamin-C and the Vitamin-C/HP-${eta}$-CD inclusion complex prepared by the solvent evaporation method. The stability of Vitamin-C was observed to increase with the decrease of temperature at a constant pressure or with the increase of pressure at a constant temperature.