Seslj was convicted of the same charge last year, and the new indictment means Seselj could be jailed for up to seven years if found guilty, regardless of the outcome of his war crimes trial.
Seselj, leader of Serbia's ultra-nationalist Radical Party, was the first suspect charged with contempt of court while on trial for war crimes at the Hague-based tribunal and was sentenced last July to 15 months imprisonment.
He has appealed that ruling, however, which related to information over three protected witnesses.
The International Criminal Tribunal for the former Yugoslavia (ICTY) said on Friday it had again charged Seselj with contempt for disclosing information on 11 protected witnesses in violation of court orders in a book he authored.
"The tribunal regards the integrity of witnesses and confidential materials as essential elements in the rule of law," the ICTY said in a statement.
In the latest contempt of court indictment, Seselj is accused of revealing the names, occupations and places of residence of 11 protected witnesses.
The disclosures are not at this stage expected to impact his war crimes trial, but judges will have a chance to comment on the matter next week.
The trial of Seselj, charged with inciting violence against Bosnians and Croatians in the former Yugoslavia during the 1990s, resumed last month after a year's delay with witnesses giving testimony behind closed doors to protect their identity.
The trial had been suspended after prosecutors said the case had been compromised by threats against a witness.
Seselj has pleaded not guilty to 15 counts for crimes between 1991 and at least 1993, including torture, murder and forced deportation of non-Serbs by his party's militia.
The latest contempt of court indictment against Seselj comes after a confidential decision by appeals judges in December overturning an earlier decision which found there were insufficient grounds to prosecute him.
A date for an initial plea hearing has not yet been set.
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