In-situ HRTEM technique was applied to various substrates and the reaction processes between substrates and molten alloy were compared. Substrates used were SiC, Si3N4, Si wafers, an amorphous carbon film, and a carbon nanotube. Ti-containing Ag-Cu eutectic alloy foil was placed on the substrate and the combined specimen mounted on the heating holder of an HRTEM and heated in the microscope to melt the alloy foil. In the case of SiC, Si3N4, carbon materials, the molten alloy spreading on the substrates were observed after melting of the alloy. SiC polar plane nano-steps appeared with the SiC dissociation by the molten alloy. On the surface of the carbon nanotube, thin film precursor spreading was observed. In contrast, Si reaction with the molten alloy produced big holes at the contacted area and molten alloy spreading was not observed.