In electronic tube manufacturing industry, indium is used for cementing glass components to form vacuum-tight seals. Owing to its low melting point (156°C) and yield strength, indium can cement together glasses with different thermal expansion coefficients or can form seals at relatively low temperature.To examine effects of plasticity of indium on formation, distribution or release of stresses in seals, bi-metallic composites were formed from strips (5×10×50mm3) of various kinds of glasses (silica glass, Kovar sealing and commercial plate glasses) by cementing with indium, and the stress was observed photo-elastically. Results were as follows: 1) Stress was nearly zero at ends and reached maximum at central parts of the composite, 2) Cooling rate after cementing did not so much affected stress in the composite, 3) By soaking at temperatures near melting point of indium, stress decreased in some degree, 4) During temperature cycles, stress showed hysteresis phenomena distinctly, 5) Observed stress near room temperature was far smaller than that calculated by assuming adhesion at melting point of indium and 6) Stress in glass caused by sticking of indium was hardly recognized.The results were explained by putting several assumptions on plastic behaviour of indium layer, namely; 1) As yield strength of indium is low, stress near free surface of indium layer in the composite cannot be intense, 2) Bending moment in the composite or expansion difference between glass strips held per unit area of indium layer are restricted by yield strength of indium, 3) Increase of stress over this limitation is prevented by plastic flow of indium, 4) The limit decreases with increase of temperature and decreases quickly to zero near the melting point of indium and 5) By soaking at constant temperature the limit decreases. Degree of lowering is slight at room temperature and is distinct at relatively high temperature.From the experimental results and the consideration described above, it is concluded that stress in the composite is mainly determined by shape or dimension of the composite including indium layer, as well as by plastic properties of indium.