Cats can eat celery safely in moderation. Celery is not toxic to cats and can actually offer some health benefits such as providing fiber for digestion, antioxidants, vitamins (A, C, K), and minerals like potassium. It is mostly water (about 95%), which helps with hydration. However, because cats are obligate carnivores, celery should only be an occasional treat and not a significant part of their diet. It should be served plain, finely chopped to avoid choking, and given in small amounts (less than 5% of their daily food intake). Too much celery can cause stomach upset, indigestion, or diarrhea. Also, avoid feeding celery seeds or celery with any seasoning or dips that may be harmful to cats.