Ehud Olmert has begun a 19-month jail sentence, becoming the first former Israeli prime minister to go to prison.
Olmert was handed a six-year sentence in 2014 after being convicted of bribery charges relating to his time as Mayor of Jerusalem.
This was reduced to 18 months in December, but an extra month was added last week for obstruction of justice.
In a video released on Monday, the 70-year-old said he "rejects outright" the bribery charges.
It came just hours before Olmert, prime minister from 2006 to 2009, was due to arrive at Maasiyahu prison in the central Israeli town of Ramle.
In March 2014 he was found guilty of accepting, while he was Mayor of Jerusalem, a 500,000-shekel ($129,000; £89,000) bribe from developers of one real estate project and a 60,000-shekel bribe in connection with another.
But the Supreme Court subsequently cleared him of the charge of accepting the 500,000-shekel bribe and reduced his sentence to 18 months.
On 10 February, the court rejected key part of a plea bargain and added one month on to Olmert's sentence after he admitted attempting to persuade his former secretary not to testify against him.
The Supreme Court is yet to rule on an appeal by Olmert against an eight-month prison sentence he was handed last year after being convicted of fraud and breach of trust for accepting illegal payments from an American businessman.