The gaze direction and face orientation of a person depicted in a portrait painting appear to follow the view-point of observers when they move parallel to the portrait. This is called the Mona Lisa effect. In this study, we examined the role of “faceness”, the degree an object looks like a face, in the Mona Lisa effect by measuring the subjective width of the depicted face. Through a series of experiments, we showed that the Mona Lisa effect is stronger for upright than for upside-down faces, but it has about the same strength for photographic negative faces as for photographic positive faces. These results suggest that the Mona Lisa effect depends on “faceness” and the configuration of facial parts (facial pictorial cues) is critical for this effect.