The Persian cat is the dumbest cat breed with its associated breeds: Himalayan and Exotic Shorthair.
The smartest is the Sphynx and Siamese. I could prattle on but it would be misleading because it is dangerous territory to claim with confidence which is the dumbest cat breed.
How do you measure cat intelligence? And it is very tricky to state that all the thousands of cats of one cat breed are dumb. It is dumb to try to do it. You won’t find the serious books on domestic cats and breeds discussing cat intelligence or if they do it’ll be with tongue in cheek.
So we have to take this sort of topic with a large pinch of salt. But people are interested in popular cat information. So websites try and please.
Years ago Animal Planet did try and rank cat intelligence. In descending order of intelligence – smartest at the top and the dumbest at the bottom – this is how they ranked the cat breeds:
Bengal (see video of Bengal cat “Hunters Moon” below)
Norwegian Forest Cat
Exotic Shorthair (short haired Persian)
Himalayan (pointed Persian)
As you can see the bottom three are cats in the Persian family. You’d probably find similar results from many websites. That does not mean they are correct, by the way.
But I’d have to pick holes in the list. There is no logic in it but there is some credibility. Somali cats are longhaired Abyssinians yet they are at opposite ends of the spectrum on intelligence. I don’t get that unless Somali breeders botched the breeding and created dumb cats while Abyssinian breeders did not. However, Siamese cats are considered by many to be smarter than other breeds. The Abyssinian too. I have seen the Sphynx and they do act smart. The Persian has been described as a piece of furniture. This means static and inactive which equals dumb. I have seen this when being photographed by Helmi Flick. While the Persian cat was inactive in front of the camera and would not become animated and therefore photogenic, the Bengal cat (one of the smart breeds) was all action and acrobatics. They interact better with humans.
However, I think it is far to say that it is more a fun list than a scientifically accurate list. Individual cats do vary in intelligence in my view. I also believe that poor breeding cat have a negative impact on intelligence. My sister adopted two British Shorthairs who must have been inbred. They were terribly slow and lacked interactability. However, it is better to assess the intelligence of individual cats rather then entire breeds of cat.