Perhaps your question was prompted by a desire for the convenience of feeding your cat and dog the same food, or as a means of saving money. If so, you've missed the mark entirely. In the long run, the veterinary bills you'll run up in treating a malnourished cat will far outnumber the small savings you might gain by feeding it dog food.
For more information on the importance of the right food for cats, please read "Why All the Fuss About Cat Food?" Or, you might be interested in enrolling in my free email class, "The Importance of Food to Your Cat's Health."