To provide a low thermal expansion alloy in which the consistency of the thermal expansion coefficient with that of a ceramics material, for example, can be optimized, to provide a low thermal expansion alloy sheet consisting of the low thermal expansion alloy, and to provide an alloy sheet for joining with a ceramics material obtained by using the low thermal expansion alloy sheet.

The low thermal expansion alloy has a composition comprising, by mass, <0.06% C, ≥20% Ni, ≥27% Co, and 50 to 70% (Ni+Co), and comprising other element of ≤2.0% in total, and the balance Fe, and has an austenite single phase structure. In the alloy, the ratio between the average thermal expansion coefficient α1 in the range from 30°C to the displacement point (TA) of the inclination of a thermal expansion curve and the average thermal expansion coefficient α2 in the range from TA to 1,000°C, α2/α1 is ≤2.1, and TA is 500 to 750°C.