In this study, the microstructure evolutions of the interface of the explosively welded cp- Ti/AISI 304 S.S composites due to heat treatment are presented. The composites were subjected to heat treatment process at various ranges of 650-950°C in argon atmosphere for 1hr. The investigations were carried out by using optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive spectrometry (EDS) and X-ray diffraction (XRD). The results reveal the presence of reaction layers in the interface and show that heat treatments cause to form different intermetallic phases at the interface. In addition, it is found that the width of the interfacial layer increases with temperature. Fractographical studies of the lug-shear test samples show the formation of river patterns and kirkendal pore structures on the Ti-side of the interface.