Katsav had denied charges he twice raped an aide when he was a cabinet minister in the late 1990s, and molested or sexually harassed two other women who worked for him during his 2000-2007 term as president.
But a three-judge panel said on convicting him in December that his testimony had been “riddled with lies.”
“When a woman says no, she means no,” the panel said in its ruling.
Katsav, 65, was also convicted of obstructing justice, for trying to confer with one complainant about her testimony to police.
Rape carries a minimum prison term of four years and a maximum of 16 years in Israel.
Katsav, who is religiously observant, had cast himself as the victim of extortion and an ethnically-motivated “witch hunt.”
Parliament elected him president in 2000 in a surprise victory over Shimon Peres.
The eruption of the Katsav affair had amplified corruption scandals that brought down Israel’s then premier, Ehud Olmert.