Lithium orthosilicate is a compound with the chemical formula Li₄SiO₄. It is a white ceramic compound, which melts congruently at a temperature of 1,258 °C (2,296 °F).

Lithium orthosilicate is of primary interest towards carbon dioxide capture, as this compound reacts with CO₂ at elevated temperatures to form lithium carbonate, and has been implemented in limited scale in such applications. Further applications of Li₄SiO₄ include solid electrolytes for lithium-ion batteries, specifically solid state batteries, and tritium breeding materials, as a component of the breeding blanket for planned fusion energy systems such as ITER.