He has sued Oops! for its May 28 cover story, which also said that the 40-year-old "Inception" actor would not recognise the baby as his, reported TMZ.
DiCaprio's lawyer has called the story "pure fantasy."
The actor is apparently demanding over USD 20,000 in damages and attorney fees. The amount is the maximum allowed under French law.
Sources said the star's team recently contacted Oops! and informed the people running the magazine that the story was false. The magazine reportedly responded that they did not care.
They were seen together at other parties too, fuelling speculations. The actor dismissed the rumour in March but the duo continued to be linked to each other.