QAnon - a far-right conspiracy theory - alleges that President Donald Trump is a secret warrior against a supposed child-trafficking ring run by celebrities and government officials. No part of the theory is based on fact.
In a blog post, Facebook said it is removing QAnon groups and pages on the platform as well as Instagram accounts that claim to be representatives.
The move escalates a policy from August which removed nearly 800 QAnon groups for promoting violence, showing intent to use weapons, or attracting followers with patterns of violent behaviour.
However, it allowed the majority of QAnon groups to stay, albeit with content appearing less often in news feeds.
Twitter also banned thousands of QAnon-affiliated accounts in July and changed its algorithms to reduce the theory's spread.
Facebook staff will now find and delete the groups and pages themselves instead of relying on user reports, the company said.
The company said it is starting to enforce the policy as of Tuesday but added it "will take time and will continue in the coming days and weeks".