The donation, equivalent to $1.1 million, “confirms our century-old friendship with the French people”, the Serbian government said in a statement.
Belgrade hopes “this symbol of French civilisation and the world will be rebuilt as quickly as possible.”
The gift comes after two tabloids, Alo and Informer, said the blaze was divine retribution after Kosovo's flag was displayed inside the cathedral during World War I centennial commemorations in Paris last year.
Serbia does not recognise the independence of Kosovo, a former southern province that broke away in a 1998-99 war.
The tabloid articles, entitled “God's punishment caught them”, were later removed, while Serbia's President Aleksandar Vucic assured that “all citizens of Serbia are sad” about the fire.
The display of Kosovo's flag inside the church, alongside those of other foreign guests at the ceremony last November, was tweeted by Serbia's ambassador to Paris but never confirmed by the cathedral or French authorities.
It was met with outrage in Belgrade, which was already angry after Kosovo's president was given a more prominent position than Serbia's at one of the centenary's events.
Hundreds of millions of euros have poured in from around the globe to help rebuild the cathedral since it went up in flames last Monday.
French President Emmanuel Macron has set a five-year deadline to rebuild the cathedral, which took around 200 years to erect.