KFC in Pontypool was given a zero score by the Food Standards Agency, the worst rating meaning urgent action is needed.
Costa in Brecon, Tesco cafe in Maesteg and Asda in Aberdare had a two rating.
That means improvement is necessary.
There are more than 26,000 businesses in Wales which have ratings, of which more than 1,400 had a two rating or below. The highest score is five.
Russel Smith, chief operating officer, KFC UK, said: “I was extremely disappointed by the rating this restaurant received, which is completely unacceptable.
“We took immediate action to return the restaurant to the standards we demand and are awaiting a re-inspection which we are sure will reflect this.”