Orsi Toth was given a spot check on July 19th and tested positive for clostebol metabolite, an anabolic steroid.
A second analysis confirmed the result, Italy's Volleyball Federation said on Wednesday.
The last picture published on Orsi Toth's Instagram account shows her with teammate Marta Menegatti, all smiles as they left for Rio a week ago. She posted the hashtag "Iamdrugfree" with the photos.
It was the third unannounced test she had been given in less than a month.
The federation at first hoped to replace her with US-born Becky Perry, according to Italian media, but because of Olympic Games entry criteria problems, they chose Laura Giombini, just two days before the first match.