The Kat Nebula, often called Planet Catnip, is a planet which is also Mr. Kat's home planet, although it is not the origination of his species; it is the fifth homeworld that the Catnipians have had to inhabit due to pollution to their four former worlds - this world is apparently on the brink of collapse as well, as they currently intend the third planet from the Sun, the old blue marble called Earth to be added to their unsurprisingly small empire. It has two huge mountains near its north pole which form the shape of a cat's head.
It seems that every Catnipian on the planet is always similar to a cat, but with a darker skin tone. At one point during Mr. Kat's stay on Earth he tried to contact it. Kat tries to contact it to get home, or to send his food there for his fellow denizens to save him or to come to Earth too to search for food.
Kat Nebula is notable for its yellow to green sky (presumably altering color dependent upon the time of day though very likely also caused by local pollutants), and thin silver rings. Its terrestrial surfaces are grey deserts, dotted with sprawling cities and metropolises with the Catnipian leader living in a tall tower within the planet's capital city. Unusually, the planet appears pink or purple from orbit yet light brown at ground level.
- Originally this planet did not belong to the Catnipians, but to an unknown race.
- The Catnipians have gained 6 known planets.
- The grey deserts and fact that the planets keep getting polluted leading to a search for a new homeworld are often references to litter boxes.
- Kid vs. Kat episode: Trespassers will be Persecuted