Katsav held a news conference Wednesday outside his home once again to protest his innocence.
"One day you will see that you buried a man alive," Katsav said.
"There is something worse than a president entering jail: an innocent president entering jail. A man is being executed today," said the former president convicted on two counts of rape and other sexual offenses in remarks carried live on Channel 10.
At approximately 10 a.m., accompanied by relatives and friends, Katsav arrived at the Ma'asiyahu Prison in Ramle to begin serving his sentence.
The former eighth president of Israel will serve his sentence in the religious wing of the prison and share a cell with former Cabinet minister Shlomo Benizri, convicted of accepting bribes.
Prison Service chief Aharon Franco said Tuesday a warden will be assigned exclusively to Katsav to ensure he does not attempt suicide.