Interdiffusion, reactions and microstructure in Ti-Cu-Ti trilayer thin films deposited on silicon wafers have been investigated by Rutherford backscattering, and cross-sectional TEM techniques in the temperature range of 350 to 500 °C. The formation of intcrmetallic compounds was found to be symmetric at both interfaces in Ti-Cu-Ti film package. TiCu compound formed first at low temperature and was followed by TiCu3 at higher temperatures. The stress in Ti-Cu film has also been measured in-situ as functions of both temperature and annealing time by thin fused quartz bending-cantilever beam technique. The stress in metallic Ti-Cu film couple on fused quartz was tensile. The stress increased as both annealing time and temperature increased and followed a parabolic relationship with time due to the growth of the intermetallic compound TiCu3 It was possible to calculate stress in the TiCu3 layer from the changes of stress in the bilayer thin film. The stress in TiCu3 was computed to be at about 3 times larger than the stress in the unreacted Ti-Cu thin film couple.