Meta Chavannes, the museum's conservator, found another painting under the work known as "Ravine," WCVB-TV reported.
Louis Van Tilborgh of the Van Gogh Museum in Amsterdam said the painting underneath appears to be one called "Wild Vegetation." It was known from a drawing Vincent Van Gogh sent his brother, Theo, but was believed to be lost.
Both paintings were done when Van Gogh was a patient in the asylum of St. Paul au Mausolee, Van Tilborgh said. He went there after cutting off part of his ear while he was living in Arles in Provence.