Abstract The reaction of sodium nitrite with silica has been investigated over the relatively wide composition range (Na/Si=0 to 10.0) below 800 °C. In an argon atmosphere, sodium nitrite reacts with oxygen to form sodium nitrate above 400 °C and decomposes to sodium oxide via other oxide species above 500 °C, irrespective of the coexistence of silica. The reaction of sodium nitrite with silica in an argon atmosphere consists of two stages. In the early stage (<600 °C), the main gaseous product is NO, while in the later stage nearly equimolar amounts of NO and O2 are formed. The early stage is further divided into two reaction processes: Process I, in which peroxide is considered to be formed in the melt by generating NO, and Process II, in which nitrate and silicates are formed by generating NO and a trace amount of O2. Peroxide is supposed to be stabilized at the solid-liquid interface, even if no silicates have been formed at relatively low temperatures. In the later stage, the reaction process or mechanism can be regarded as similar to that of sodium nitrate with silica, as the concentration of nitrite in the melt is very low.