The media tycoon and two of his children tested positive for the virus on Wednesday after holidaying in Sardinia, where the infection rate is higher than in much of Italy.
On Thursday he was staying near Milan.
“A small precautionary hospitalisation was needed to monitor the progress of Covid-19 but he is fine,” said Forza Italia senator Licia Ronzulli.
Berlusconi was transferred to an isolation ward at San Raffaele Hospital on Thursday night, from his villa at Arcore, just north of Milan.
Earlier his personal doctor Alberto Zangrillo described him as asymptomatic.
Italian media report that Berlusconi’s 30-year-old partner, Marta Fascina, has also tested positive for the virus. Ms Fascina, a Forza Italia MP, has been in self-isolation with him.
Berlusconi sent a phone message to party activists in Genoa on Thursday saying “I’m continuing to work as best I can on the current election campaign”. Separately, he said he did not know how he had caught the virus.