Police in Rome declined to offer an estimate for the crowd, but the PDL said more than one million people had turned out in response to an anti-Berlusconi rally in Rome last week.
Series of setbacks
Berlusconi's address to his supporters came after a series of setbacks for the prime minister.
His party was excluded from the country's March 28-29 ballot in the key Rome province, which has more than two million voters, after it failed to register in time.
The error could hurt his party's chances in an election seen as an important test of strength for Berlusconi's government.
Berlusconi is also currently under investigation for abuse of power, after phone taps showed him allegedly trying to block political talk shows on state television that were critical of his government.
He is also facing trials for tax fraud and bribery. Berlusconi has denied any wrongdoing.
Berlusconi's battles with the law have marked his public life since he burst on to the political scene in the mid-1990s.
The former media tycoon has faced charges including corruption, tax fraud, false accounting and illegally financing political parties.
Meanwhile new laws are going through parliament which would have the effect of keeping Berlusconi out of the courts.
One would allow the prime minister or any member of his cabinet to be automatically granted the suspension of legal process for at least 18 months.
Passed by the lower house after a stormy debate, it is to be debated by the senate on March 9.
More legislation would quash any legal action if a final verdict is not handed down within six years of it being launched - which would end a large number of ongoing cases, not just those against Berlusconi.