Preparation of rice husk ash with high specific surface area and chemical reactivity of the product are reported in this paper. The amorphous rice husk ash with high specific surface area of 311 m(2.)g(-1) was produced by heating acid treated rice husk at 700degreesC for 4 h. The isotherms of rice husk ash are similar in shape to type 1[ of Brunaner's classification with mesopores. being predominant. The rice husk ash has a high chemical reactivity, especially that pretreated with acid. This chemical reactivity depends on ashing temperature and pretreatment conditions. There is an exponential relation between the specific surface area of rice husk ash and the change in the conductivity of saturated Ca(OH)(2) Solution With rice husk ash, from which the specific surface area can be known according to the conductivity change.