The large drawing has been held since 1862 in the huge collection of Renaissance art at the Conde Museum at the palace of Chantilly, north of the French capital.
Still, experts are cautious about attributing the work to da Vinci.
Scientists have managed to date the Monna Vanna to around the start of the 16th century, which matches the lifetime of da Vinci, who died in 1519.
So there is a nude charcoal portrait and the woman is known as the Mona Vanna.
However, after a series of tests at the Louvre Museum in Paris, experts now have strong reasons to believe that Leonardo worked on both.
Among the signs, according to curator Mathieu Deldicque, are the fact the drawing was made during the same period as the Mona Lisa, the paper is from the same region of Italy, and the technique is very similar to that of the Mona Lisa.
'It is nearly certainly a preparatory work for an oil painting, ' Deldicque said, suggesting there is a close connection to the Mona Lisa. Leonardo drew with his left hand, ' he said.
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The Mona Lisa oil painting, among the world's greatest art treasures, hangs in the Louvre.
He also said that the hands and body on both the Monna Vanna and the Mona Lisa are nearly identical and that both portraits are nearly the same size. Bruno Mottin said tests had revealed the high-quality work was not a copy of a lost original.
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Officially attributing the painting to da Vinci 'is job that is going to take some time, ' he added.
It is a very hard drawing to work on because it is particularly fragile, ' he added.
But Mottin said experts hoped to pin down the identity of the artist within two years, in time for an exhibition at Chantilly to celebrate the 500th anniversary of Leonardo da Vinci's death.
There's something vaguely familiar about this charcoal sketch of a woman's face and nude torso - could it be an unclothed precursor to the Mona Lisa?
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