He told reporters he was "completely innocent" and hit out at the trial as a "circus".
Kepiro is still number one on the Simon Wiesenthal Center's latest list of most wanted Nazi war criminals.
He is accused of "complicity in war crimes" in a raid by Hungarian forces on the northern town of Novi Sad between January 21 and 23, 1942.
The exact charges will not be known until they are read out in court, but prosecutors have said he will be charged with having ordered the rounding up and execution of 36 people.
The director of the Center Efraim Zuroff, Serbian war crimes prosecutor Vladimir Vukcevic and representatives of the Jewish community of Novi Sad will attend the opening of the trial.
"This is the first trial of a Hungarian war criminal and since Hungary has collaborated with Nazi Germany, it's very important it takes place," Zuroff told reporters.
Outside the court, around 30 students were demonstrating, wearing yellow Stars of David and brandishing banners and placards with phrases such as "How do you sleep Mr. Kepiro?" and "Murder has no age".
"There can be no clemency, no sympathy and no ignoring of the facts," Zuroff said.
Kepiro has admitted his presence at the Novi Sad raid, but insists he knew nothing of the massacres.
"The charges are lies, all lies," he told reporters. "I knew nothing of the massacres. The soldiers told me nothing."
Kepiro has already been found guilty -- in absentia -- of the crimes in Novi Sad twice, in 1944 and then again in 1946, this time under the communists, when the previous 10-year jail sentence was quashed.
Sentenced to 14 years, he avoided prison by fleeing to Argentina where he remained for half a century before returning to Budapest in 1996 where Zuroff tracked him down 10 years later.
"I hope ultimately he will be convicted and punished. It's very important, especially in Hungarian society, seeing the problem it faces with extreme right, racism and anti-Roma sentiment," Zuroff said.