Excavating the ground which consists of the marine deposits formed during Neogen and/or Quaternary period, the acid sulfate soil occasionally appears on the execution basis. As this soil includes sulfuric acid produced with the oxidation of sulfide, the growth of plants is disturbed and it becomes difficult to improve the soil by adding a stabilizer. In general, the calcic materials such as stone powder and zeolite have been employed to neutralize the acid sulfate soil from the past. Therefore, the shells which are composed mainly of a calcium carbonate can also be considered to be useful as a material for the neutralization process. We have ascertained the stabilization effect due to the using of crushed oyster shell by comparing the amount of swelling and CBR value for soil-stabilizer-shell mixture with those for soil-stabilizer mixture. Mixing crushed oyster shell into the soil, pH value of the mixture gradually shifted to neutral with elapsed time and its water content decreased immediately. Furthermore, the amount of swelling which occurred during submergence curing was extremely small for soil-stabilizer-shell mixture and CBR value of this mixture was 1.5 to 4 times larger than that of soil-stabilizer mixture. These results indicate that both surplus soil and non-industrial waste will be utilized effectively as embankment and subgrade materials at a time.