Cat urine smells like ammonia because cat urine contains urea. Urea is a waste product of protein breakdown. Cats are big protein eaters. Bacteria breaks down the urea and this is what releases ammonia and the along with it the strong smell that is often associated with cat litter. You could try feeding your cat a different source of protein to see if that makes a difference. To help combat the ammonia smell, litter needs to be changed frequently. If the ammonia smell if very strong or has changed and is now noticeably stronger than usual see your vet for advice. The only way to really get rid of the ammonia smell is to use an enzyme cleaner to remove cat's urine. Note: This is also the same science behind the use of the bio-enzymatic system used in Nature's Miracle Intense Defense Litter. This is a very good article which explains exactly how to remove cat urine and what should be used (also talks about using vinegar and baking soda).