Wetting behavior at the Al/a-Al 2 O 3 liquid/solid interface is closely correlated with oxygen-induced structural changes at the interface. However, direct experimental evidence for the possible interfacial modifications has been rare. In the present study in situ high-resolution electron microscopy is successfully employed to characterize the structure of the interfaces between liquid Al and a-Al 2 O 3 with [0 0 0 1] and [ 1 1 0 2] surface normal directions at an elevated temperature. We provide evidence for ordering in the liquid (i.e. ordered oxygenrich liquid interfacial layers) at both interfaces. The liquid at the Al/a-Al 2 O 3 (0 0 0 1) interface shows density perturbations in the direction perpendicular to the interface (layering) with a periodicity close to the interplanar distance of the (0 0 0 6) planes of a-Al 2 O 3 . On the other hand, the liquid at the Al/a-Al 2 O 3 ( 1 1 0 2) interface also reveals layering with an interlayer spacing of $0.25 nm and, additionally, with a degree of order occurring within the first few liquid layers (in-plane ordering), the ordered structure of which is similar to Al 2 O rather than a-Al 2 O 3 .