Improving the corrosion resistance of magnesium-lithium (Mg-Li) alloys is pivotal for expanding their prospective utilization in lightweight structural materials. This research focused on evaluating the corrosion inhibition effectiveness of a composite corrosion inhibitor comprising sodium fluoride (NaF) and caffeic acid (CA) on the LAZ931 alloy in a 3.5 wt.% NaCl solution. The results demonstrated that NaF alone is insufficient to prevent localized corrosion of the alloy. Remarkably, the addition of 0.001 M caffeic acid to a 0.05 M NaF solution significantly increased the corrosion inhibition efficiency from 54.36 % to 88 %. This substantial improvement in corrosion resistance can be credited to the formation of the dense protective NaMgF₃ deposition products on the sample surface. This study offers a novel approach to the design of corrosion inhibitors for duplex Mg alloys, emphasizing the synergistic effect between NaF and CA in augmenting corrosion protection.