The button will let people hide comments on their Facebook pages and also provide feedback about them.
The feature is only for use in the US at the moment.
The move has long been anticipated – and demanded by users – but the social network says it is not a ‘dislike’ button.
“We are exploring a feature for people to give us feedback about comments on public page posts. This is running for a small set of people in the US only,” the company said in a statement.
The news was released via news site Tech Crunch.
When the downvote button is clicked, the selected comment is hidden. Users can then decide whether to flag a post as ‘offensive’, ‘misleading’ or ‘off-topic’.
Previously, Facebook’s creator Mark Zuckerberg has ruled out adding a dislike button to the social media giant’s site, claiming that would not help the kind of online community the company is trying to create.
Martin Garner, a tech analyst at CCS Insight, said the button could be a part of Facebook’s strategy to resist labelling itself a publisher.
“It has become very clear that Mark Zuckerberg doesn’t want Facebook to have the responsibility of identifying what is offensive or misleading – and what is not – because that would put him into the position of being a publisher rather than a platform,” said Garner.
Also on Friday, it was announced that Facebook was doubling the number of engineers it employs in London.
However, the company did not say how many more engineers it would use.