This study was conducted to reuse the rice straw ash as washing agent for oil contaminated soils. The results are summarized as follows. The physical characteristics of rice straw before and after burning were as follows ; In case of burning rice straw 1g, the rice straw ash was generated 0.14g and pH was changed neutrality into alkali(pH 10.9) and specific surface area was increased to five times and particle distribution was corresponded to fine silt(under 0.05㎜) The physical charateristics of rice straw ash were Carbon 10.9%, Hydrogen 1.5%, Oxygen 23.4%, Nitrogen 5.2%, Sulfate 1.2% and chemical charateristics were Si 189.2ppm, Ca 10.2ppm, Mg 4.7ppm. Oil cleanup ratio by pH varation were about 40～50% of initial concentration of oil by pH 10～11. As the result of cleanup comparative experiment, the rice straw ash was about 20～30%, the tritonX-100 about 40～50% of washing efficiency, and then in the future it will be possibility of substitute washing agent.