It was one of the biggest one-day losses in US corporate history.
At the start of the day, Facebook was valued at $630bn (£481bn). By the end, it had dropped to $510bn (£389bn).
Company founder Mark Zuckerberg personally lost more than $15bn (£11.5bn) in one day, seeing him fall from fourth to sixth on Forbes' list of global billionaires.
The drop came after the social media giant published its second quarter results.
Although still positive, they came in below investor expectations - and company shares had plummeted nearly 20% by the end of the day.