Olmert arrived Monday morning at the Maasiyahu prison, where he will be confined in bloc 10, dubbed by the Israeli media as the "VIP wing."
"Life is offering me today no simple test," Olmert said in a video message from his home before a convoy took him to prison. "I go toward it with great sadness."
The 70-year old who served as premier from 2006 until 2009 said he had "made mistakes" but argued his actions were "not criminal." He denies taking bribes.
In 2014, a court convicted Olmert of taking kickbacks in a real estate rezoning scandal when he was mayor of Jerusalem between 1993 and 2003. Several other high-level officials were also implicated in the so-called Holy Land real estate affair.
That conviction related to attempts by Olmert to convince his former secretary, Shula Zaken, to keep quiet and not accept a plea deal in a separate corruption case. After initially agreeing, Zaken later produced recordings showing Olmert had tried to persuade her not to cooperate with prosecutors.
As prime minister, Olmert relaunched peace talks with Palestinians, which had been frozen by Olmert's predecessor, Ariel Sharon. Some have suggested that the charges against Olmert came about because the Israeli far-right opposed his overtures towards the Palestinians.
Given Olmert's knowledge of state secrets, he will receive special treatment. Former President Moshe Katsav is also serving time at Maasiyahu on sexual harassment and rape charges.
cw/rc (AFP, AP, dpa)