Ten activists entered the Portuguese chicken restaurant in Duke Street, Brighton holding laptops and wearing chicken masks.
A spokeswoman from the protest said: “The aim of the action was to disrupt the customer’s meals and to draw attention to the violence and suffering that went into it.
"We know that people don’t like to be exposed to the truth of their food, especially while they are eating it, but what these animals go through is unacceptable and we cannot ignore that so many innocent beings are suffering this very second.”
After a 20-minute protest, activists left the building chanting: “What do we want? Animal liberation. When do we want it? Now!”
The action is part of a national week of action called Occupy Nando’s after an investigation by a group called Surge.
A Nando’s spokesperson said: “We can confirm that there was a small organised disturbances in one of our Brighton restaurants on Wednesday night and we are sorry for those customers who had their meals interrupted.
"We worked with the police to minimise any disruption in a peaceful way and allow our customers to enjoy their meal and have a great night.”