Watson, who released a range of vegan ready meals in Waitrose and Ocado earlier this year, Tweeted: "Who poses for an anti-fur campaign with PETA and then WEARS FUR? Just shows the intentions with the campaign were never for the animals in the first place."
The star then retweeted a video from animal-rights organization PETA of a cow raised for leather being struck to the head several times with a sledgehammer.
Though Watson did not specify which celebrity she was talking about, many people guessed it was aimed at reality TV star Khloe Kardashian, while others suggested it could be singer Alexandra Burke.
This isn't the first time Watson has spoken out about animal-rights.
Last year, she appeared on the UK breakfast show This Morning to challenge a farmer who let customers name their turkeys over what he meant by 'humane slaughter'.
"I disagree with the killing of animals full stop, but in a way, it's good because I want people to be able to make a connection with these animals and make people realize they have souls and they're gentle creatures," Watson said.