Abstract: Mo foil and Al foil were joined by diffusion bonding at 600℃ and 20 MPa for holding 50 min to 6 h to study the evolvements of the interface reactions at Mo-Al solid-solid interface. The results show that the new phases nucleate and form beneath the Mo substrate skin layer of 0.5-0.7 μm, then teare and lift off the Mo skin, turn to be island-like, and grow into Al substrate with Mo skin sandwiched.Initially, the reaction layers are not plane and like islands distributing along the interface, of which the growing rate is faster in longitudinal than in horizontal;with the islands further growing and joining together, three layers, Mo₃Al₈, MoAl₅ and MoAl₁₂, arise in sequence from Al-Mo interfacial reaction.When Al element is consumed, MoAl₄ phase grows up and forms a new layer between Mo₃Al₈ layer and MoAl₅ layer.At last, MoAl₁₂ and MoAl₅ are consumed and disappear with Mo₃Al₈ layer and MoAl₄ layer left on the interface.