The organisation wants companies to do more to help keep the streets clean.
The survey found that burger wrappers, sauce sachets and plastic straws made up a lot of the rubbish.
Litter from McDonald's made up more than a quarter (29%) of all the fast food rubbish, then packaging like chip trays and plastic forks from local fast food restaurants made up 21%. And pasty and pie wrappers from Greggs made up 18% of litter.
Phil Barton, from Keep Britain Tidy, said companies should do more to encourage people not to drop litter.
He said: "We want all fast food chains to reduce unnecessary packaging and make it easier for customers to do the right thing."
A spokeswoman for McDonald's said plenty of bins were provided, and customers were encouraged to throw away their litter responsibly.