Aluminum-based amorphous alloys containing transition and rare-earth metals have been actively studied in recent years due to their high mechanical and corrosion properties. Advanced anticorrosion protective coatings are already being developed based on such compositions. However, the question of the influence of various rare-earth metals and the concentration of transition metals on the maximum increase in service characteristics of these alloys remains unresolved. Amorphous ribbons of Al–Ni–Co–Sm(Tb) compositions with different Ni/Co ratios are prepared by planar flow method. The ribbons are 5 mm wide and 40–45 µm thick. Their corrosion behavior in a 5% NaCl solution over 1500 h is studied. The corrosion rate of amorphous ribbons, as well as the depth corrosion index, is calculated from gravimetric and chemical-analysis data. It is found that compositions with a high cobalt content have greater corrosion resistance. As a result of interaction with a corrosive medium, a stable aluminum-hydroxide layer is formed on the surfaces, which ensures their stability. It is shown that the mechanism of the corrosion process is determined by the reactivity of alloy components and significantly different solubility of the resulting hydroxide layers of components of Al–Ni–Co–Sm(Tb) amorphous alloys.