Private individuals will no longer be allowed to advertise guns on Facebook and Instagram, the photo-sharing service owned by Facebook.
Facebook had already banned the sale of guns without identity checks, but the new rules aim to stop all gun trade between individuals on the sites.
The move comes three weeks after US President Barack Obama unveiled new restrictions on gun purchases.
The rule change brings gun sales under the same restrictions placed by Facebook on illegal drugs and pharmaceuticals by Facebook.
The site has 1.59 billion users worldwide.