Vietnam is an agricultural country, which produces lot of rice and its by product is rice husk ash (RHA). The RHA is considered as waste in agriculture, and treated by burn in the open air. This process causes air pollution, thus attracted Vietnamese researchers to find alternative method to reduce the impact of rice husk ash on environment. The research group in Department of Ceramic Materials aims to reuse rice husk ash as source of silica (SiO2). It needs to emphasize that the main content of rice husk ash is silica. This research reports new technology to mixing RHA and CaO with the Ca/Si molar ratio of 1.0, in order to synthesize calcium silicate hydrate (CSH) such as tobermorite (C5S6H5) and xonotlite (C6S6H) as environmental materials. The advantage of our study is to utilize the Vietnam RHA and to reduce the environmental impacts by using hydrothermal treatment technique. Key words: Calcium silicate hydrate, rice hush ash, hydrothermal treatment, ceramic.Vietnam is an agricultural country, which produces lot of rice and its by product is rice husk ash (RHA). The RHA is considered as waste in agriculture, and treated by burn in the open air. This process causes air pollution, thus attracted Vietnamese researchers to find alternative method to reduce the impact of rice husk ash on environment. The research group in Department of Ceramic Materials aims to reuse rice husk ash as source of silica (SiO2). It needs to emphasize that the main content of rice husk ash is silica. This research reports new technology to mixing RHA and CaO with the Ca/Si molar ratio of 1.0, in order to synthesize calcium silicate hydrate (CSH) such as tobermorite (C5S6H5) and xonotlite (C6S6H) as environmental materials. The advantage of our study is to utilize the Vietnam RHA and to reduce the environmental impacts by using hydrothermal treatment technique.Key words: Calcium silicate hydrate, rice hush ash, hydrothermal treatment, ceramic.