It is the second time in a year the frail elder statesman has received hospital care.
Chirac, who led France from 1995 to 2007, was "hospitalised this morning at Pitie-Salpetriere (hospital in Paris) to be treated for a lung infection," his son-in-law Frederic Salat-Baroux told AFP, adding he would remain there "in the coming days."
The popular ex-president had just returned from a visit to Morocco with his wife Bernadette, Salat-Baroux added.
Rumours were swirling about his condition but a source close to the family told AFP he was conscious.
The centre-right Chirac, who served two terms as head of state, is probably best remembered internationally for his opposition to the US military intervention in Iraq in 2003. A small stroke while in office in 2005 weakened him, and he is now rarely seen in public.
In December 2015, he spent two weeks in hospital, suffering from what his family described as fatigue. In recent weeks, his entourage said his health had improved.
Chirac has reportedly suffered from a degenerative neurological disorder in recent years, leading prosecutors to spare him the embarrassment of having to appear in court during his 2011 corruption trial.
He was handed a two-year suspended prison term for colluding in the creation of 28 fake jobs for party workers when he served as mayor of Paris mayor.
Benefiting from a popularity that extended beyond the right -- he flirted with communism in his youth -- Chirac also served two stints as prime minister in 1974-76 and 1988-90 and was Paris mayor from 1977-1995.
His influence is still felt in French politics, with one of his former prime ministers and political heirs, Alain Juppe, the current favourite to win next year's presidential election.
Polls make Juppe the favourite to win the conservative nomination, ahead of former president Nicolas Sarkozy.
Both rivals tweeted Sunday their concern and best wishes for Chirac's prompt recovery.
"I am thinking affectionately of Jacques Chirac. I hope with all my heart he overcomes his illness and gets well soon," Juppe tweeted.
Sarkozy also took to Twitter, saying: "I am thinking at the moment of
Jacques #Chirac. I hope he recovers as quickly as possible."