Ehud Olmert will become the first former Israeli prime minister to go to jail, after Israel's Highest Court of Justice upheld one count of bribe-taking in a appeal ruling today.

The court in Jerusalem acquitted Olmert of one major count of bribe-taking when he served as mayor of the city between 1993 and 2003.

But it upheld a conviction for a lesser count and dramatically reduced a prison sentence handed to Olmert in May 2014 by Tel Aviv's district court from six years to 18 months.

Olmert, who was premier between 2006 and 2009, is to start his sentence on Feb 15.

The dramatic ruling crowns eight years of legal proceedings, which toppled Olmert and thereby slammed the door to the furthest-reaching peace negotiations ever with the Palestinians.

Olmert, a former right-wing nationalist ideologist who became more pragmatic, centrist and dovish later in life, was succeeded by current hardline Prime Minister Benjamin Netanyahu in 2009 elections held after his resignation over the corruption allegations.

"I've said in the past, that I was never offered, and that I never received bribes and I say this also today," the 70-year-old told reporters after the long-awaited appeal ruling.

"A large stone has been removed from my heart," he said of the partial acquittal, but added, "I respect the decision of the Supreme Court judges," to uphold the conviction of the smaller count of bribe-taking.

Olmert was acquitted of accepting 500,000 Israeli shekels (US$130,000) in one count of bribe-taking, by a majority of four judges against one, a court statement said.

The money had been given to his brother by a businessman who had become a state witness while in his 70s and in poor health and who then died in the midst of the trial, making the count not clear-cut, the supreme court said.

The second count involving 60,000 shekels given to aides of Olmert was unanimously upheld.

The lower Tel Aviv court had said that Olmert had abused his senior position to promote his personal interests and, via his brother and aides, received huge sums in exchange for pushing through the real-estate project.

"The last few years were difficult as a result of a dark cloud hovering over my life, every day, every hour, and over that of my family, my wife, my five children and my 11 grandchildren," Olmert said.

Attorney Roi Belcher said he was "happy" that the supreme court accepted some of his main arguments that had previously been rejected by the Tel Aviv district court, which had sentenced Olmert to six years jail.

A dozen other senior officials were also convicted in the major real-estate case, in which public figures accepted bribes from contractors to promote a construction project in Jerusalem known as Holyland.

The most severe sentence was handed to the Jerusalem municipality chief engineer from 2000 to 2005, Uri Shitrit, who received seven years in jail for accepting bribes. That sentence was upheld in full in today's appeal ruling.

The Tel Aviv court had said in its March 2014 verdict that two counts of indirect bribe-taking on behalf of Olmert had not passed the statute of limitations and were sufficiently proven.

Olmert has also become entangled in several other corruption scandals.

While critics say that he is one of many politicians who gave preference to his own enrichment and personal interests over that of the public, supporters charge that hardliners opposed to his peace moves with the Palestinians had deliberately sought to topple him.

"Something important happened in Israel today. A former prime minister will go to jail, convicted of one of the most serious offences in our penal code, of bribery," said prosecution attorney Yaron Golomb.

"Even though the sum is smaller, this is still a bribery conviction of 60,000 shekels."

He quoted supreme court Judge Neal Hendel as saying: "The day that a person who held the highest position in the country goes to jail will be a dark day. The public feels like a child betrayed by those elected to lead and serve as a personal example."

- dpa