Lady with an Ermine is one of Poland's national treasures. The portrait's subject is Cecilia Gallerani, painted at a time when she was the mistress of Ludovico Sforza, Duke of Milan, and Leonardo was in the Duke's service. It is one of only four portraits of women painted by Leonardo, the others being the Mona Lisa, the portrait of Ginevra de' Benci, and La belle ferronnière. The painting of Lady with an Ermine was donated on 29 of December 2016 to the Polish Nation via the Ministry of Culture by Prince Adam Karol Czartoryski the last direct descendant of Princess Izabella Czartoryska, and the last private owner.and has been on display in the museum's main building since 2017.
The painting shows a half-height figure, the body of a woman turned at a three-quarter angle toward her right, but with her face turned toward her left. Her gaze is directed neither straight ahead, nor toward the viewer, but toward a "third party" beyond the picture's frame. Gallerani holds a small white-coated stoat, known as an ermine. Her dress is comparatively simple, revealing that she is not a noblewoman. Her coiffure, known as a coazone, confines her hair smoothly to her head with two bands of it bound on either side of her face and a long plait at the back. Her hair is held in place by a fine gauze veil with a woven border of gold-wound threads, a black band, and a sheath over the plait.
There are several interpretations of the ermine's significance. In its winter coat, the ermine was a traditional symbol of purity, as it was believed it would face death rather than soil its white coat. In his old age, Leonardo compiled a bestiary in which he recorded:
MODERATION The ermine out of moderation never eats but once a day, and it would rather let itself be captured by hunters than take refuge in a dirty lair, in order not to stain its purity.
He repeats this idea in another note, "Moderation curbs all the vices. The ermine prefers to die rather than soil itself." Ermines were kept as pets by the aristocracy and their white pelts were used to line or trim aristocratic garments. For Ludovico il Moro, the ermine had a further personal significance in that he had been in the Order of the Ermine (Naples) in 1488 and used it as a personal emblem. The association of the ermine with Cecilia Gallerani could have referred both to her purity and to make an association with her lover. Alternatively, the ermine could be a pun on her name: The Ancient Greek term for ermine, or other weasel-like species of animals, is galê (γαλῆ) or galéē. This would be in keeping with Leonardo's placement of a juniper bush behind the figure in his portrait of Ginevra de Benci in reference to her name. Given that Gallerani gave birth to a son acknowledged by Lodovico in May 1491, and the association of weasels and pregnancy in Italian Renaissance culture, it also is possible the animal was a symbol of Cecilia's pregnancy. In addition, it has been speculated that the animal in the painting may not be an ermine,but a white ferret, a colour favoured in the Middle Ages because of the ease of seeing the white animal in thick undergrowth.