He was sentenced to four years in prison for tax fraud last year, commuted to four hours' work a week with elderly dementia patients.
The care home said the 77-year-old would be treated like any other worker.
As he arrived, Berlusconi was heckled by a trade unionist in a clown hat who shouted: "To prison!"
"We Italian workers have one dream in our hearts: Berlusconi in San Vittore!" he yelled, referring to a prison in Milan.
He was eventually taken away by police.
Mr Berlusconi made no comments to reporters outside the home after completing his first day of service.
The three-time former prime minister wore a navy blue suit with a badge from his centre-right Forza Italia party.
The BBC's David Willey in Rome says that he had been warned not to seek publicity or political advantage from the work.
The billionaire has been embroiled in a string of court cases.
He was convicted last year of buying TV rights at inflated prices via offshore companies to avoid paying taxes in Italy.
But he was spared prison because of his age.
Berlusconi chose community service rather than house arrest to serve out his commuted sentence.
Our correspondent says this will enable him to continue to lead Forza Italia in the European elections, although he was forced to resign his seat in the upper house of parliament.
Berlusconi has also had to surrender his passport and his travel within Italy is severely restricted.
He also has to observe a nightly curfew at his palatial home near Milan.
Berlusconi is said to have been studying Alzheimer's disease in preparation for his community service.
Massimo Restelli, head of care services there, told La Repubblica newspaper that Berlusconi's introduction would be "gradual" so that he and the elderly patients could get used to each other.
"It will be small steps so as not to make any mistakes, and then he could do all sorts of things," he said.
"He could help with meals, which are tricky because sometimes you have to 'remind' the patient that they are eating."
He said Berlusconi would be accompanied at all times by a medical worker specialised in Alzheimer's.
"We'll see if Berlusconi's presence creates some kind of close bond, if he is a reference for anyone," he added.
Berlusconi has always denied the charges against him, accusing left-wing judges of a witch-hunt.
Last year he was convicted of paying for sex with an underage prostitute and abusing his powers, which brought him a lifetime ban from public office.
He is appealing against the underage sex conviction, in a trial known as the "Ruby" case.
He is also on trial for allegedly bribing a centre-left senator to switch sides.
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