For three days, an ad will appear at the top of users' news feeds linking to advice on "how to spot fake news" and report it.
The campaign, which will be promoted in 14 countries, is "designed to help people become more discerning readers", the social media firm said.
But experts questioned whether the measure would have any real impact.
"Until Facebook stops rewarding the architects of fake news with huge traffic, this problem will just get worse," Tom Felle, a lecturer in digital journalism at City University told the BBC.