The porous silicon was prepared in the condition of 70mA/cm2 and 5.10 sec and then oxidized at 800~110$0^{circ}C$ MOS(Metal Oxide Semiconductor) structure was prepared by Al electrode deposition and analyzed by C-V (Capacitance-Voltage) characteristics. Dielectric constant of oxidized porous silicon was large in the case of low temperature (800, 90$0^{circ}C$) and short time(20-30min) oxidation and was nearly the same as thermal SiO2 3.9 in the case of high temperature (110$0^{circ}C$) and long time (above 60 min) It is though to be caused byunoxidized silicon in oxidized porous silicon film and capacitance increase due to surface area increment effect,