Krajisnik is one of the most senior figures to have been tried at the ICTY
The International Criminal Tribunal for the former Yugoslavia has cut seven years off the prison sentence of former Bosnian Serb leader Momcilo Krajisnik.
Appeals Chamber judges overturned Krajisnik's convictions for the murder, extermination and persecution of non-Serbs during the 1992-95 Bosnian war.
But he must still serve 20 years in jail for the deportation, forcible transfer and persecution of civilians.
Krajisnik was a close aide to ex-Bosnian Serb leader Radovan Karadzic.
In November, Mr Karadzic, who faces 11 charges of genocide, war crimes and crimes against humanity, testified as a defence witness at Krajisnik's appeal.
He argued that Krajisnik, also a former speaker of the Bosnian Serb parliament, was "not a member of the presidency" during the war.
When he was convicted of war crimes and imprisoned in 2006, Krajisnik was the most senior political figure from any conflict in the former Yugoslav republics to have been found guilty by the ICTY.
The Bosnian war left about 110,000 people dead and displaced millions
Although the court said there was "insufficient evidence" to prove charges of genocide and complicity in genocide, it found him to have been part of a joint criminal enterprise that carried out the extermination, murder, persecution and deportation of non-Serbs.
Krajisnik's role in the commission of the crimes was crucial, if found. The Bosnian war left about 110,000 people dead and displaced another 2.2 million.
But on Tuesday, the ICTY Appeals Chamber at The Hague quashed the convictions of "murder, extermination and persecution, other than that based on deportation and forcible transfer".
"The trial chamber committed a legal error in failing to make the findings necessary for Krajisnik's conviction," Judge Fausto Pocar said.
But the Appeals Chamber upheld earlier guilty verdicts for the "deportation, forcible transfer and persecution based on these crimes" of non-Serb civilians and sentenced him to 20 years in prison.
It said the testimony given by Mr Karadzic in defence of his former aide had not been "sufficient to undermine the extensive evidence" of the seniority and control he had exercised during the conflict.
The new sentence, which Judge Pocar described as "severe and proportionate", will take into account time Krajisnik has spent in custody since April 2000.
Since its inception 15 years ago the Tribunal has indicted 161 persons for war crimes committed on the territory of the former Yugoslavia. Forty-eight individuals have been convicted.