The Senate proceedings cap a disastrous week for the 77-year-old billionaire, who was forced into a humiliating climbdown on Wednesday by a party revolt which made him back centre-left Prime Minister Enrico Letta in parliament.
After pulling his ministers from the coalition government at the weekend and calling for new elections, Berlusconi had to reverse his decision to bring down the government and, instead, backed Letta in a confidence vote after dissenters in his own party threatened to tear the centre right apart.
The revolt left Berlusconi's People of Freedom (PDL) divided into two blocs, with 42-year-old party secretary Angelino Alfano heading a group of moderates while a hardcore of loyalists remain with Berlusconi, although a formal split has not yet been confirmed.
Even if Berlusconi is expelled from the Senate he could still lead the center-right, or the part of it that remains loyal to him, from outside parliament.
However, his position would be weaker and he would be robbed of the protection from arrest which parliamentarians enjoy, which could be important as he faces many other legal cases.
Berlusconi's political future has been under threat since early August when Italy's top court rejected a final appeal and found him guilty of a massive tax fraud scheme at his Mediaset television empire.
It sentenced him to four years in prison, commuted to one year under house arrest or in community service, making him ineligible for parliament under a law passed last year.
Berlusconi loyalists insist this law should not apply in his case because the offences occurred before it was passed.