Dawnette Knight, 34, pleaded no contest to stalking and making criminal threats against the Welsh actress. She was found guilty by a Los Angeles Superior Court judge.
Knight, who was in love with the husband of the actress, Michael Douglas, sent dozens of threatening letters and made harassing telephone calls to the couple.
Zeta-Jones was not present in court, but she did submit a letter to the judge, in which she called Knight "simply evil" and said her actions "will be with me for the rest of my life."