A reflective Ag alloy film for reflectors, which has excellent surface flatness and shows high reflectivity even under a heating environment and a reflector.The reflective Ag alloy film for reflectors has an average surface roughness of 2.0 nm or less and contains a rare earth element (such as Nd) in a content in the range of 0.1 to 3.0 at %, or further at least one selected from Au, Pd, Cu and Pt in a content in the range of 0.5 to 5.0 at %. The reflector comprises the above reflective Ag alloy film formed on a substrate.