Interfacial characteristics of molten Bi-43Sn alloy on amorphous and crystalline Fe 78 B 13 Si 9 during wetting were investigated at 523 K, 573 K, 623 K and 673 K. It is found that an intermetallic compound exists at the interface of Bi-43Sn alloy on amorphous Fe 78 B 13 Si 9 , while no intermediate reaction layer is formed at the interface of Bi-43Sn alloy on crystalline Fe 78 B 13 Si 9. For Bi-43Sn alloy/ amorphous Fe 78 B 13 Si 9 system, isothermal aging was performed at 323 K, 373 K and 423 K. The layer growth of the intermetallic compound is mainly controlled by a diffusion-controlled mechanism in the temperature range studied because the values of time exponent (n) is approximately equal to 0.5.