Mildly toxic — irritant
Mildly to moderately toxic — but, despite the name, a peace lily is NOT a true lily and does not cause the kidney failure that real lilies do in cats. It irritates the mouth with calcium oxalate crystals.
Peace lilies (Spathiphyllum) are a frequent source of confusion. They are not true lilies, so they do not carry the deadly kidney risk that Lilium and Hemerocallis pose to cats. Instead, like pothos and philodendron, they contain insoluble calcium oxalate crystals that cause burning and irritation of the mouth and throat when chewed. It is painful and causes drooling and swelling, but is rarely life-threatening.
Both dogs and cats get the same oral-irritation reaction. The key reassurance for cat owners: a peace lily will not destroy your cat’s kidneys the way a true lily can — but a true lily is a separate, far more dangerous plant.
Rinse the mouth and offer water; the discomfort usually eases within hours. Call your vet if swelling is significant, breathing or swallowing is affected, or vomiting persists. If you are unsure whether you have a peace lily or a true lily (especially with a cat), treat it as a true-lily emergency and call a poison helpline immediately.
Related: Are TRUE lilies toxic to cats? · Is pothos toxic? · Is philodendron toxic?
General information, not veterinary advice. If your pet has eaten a toxic plant or shows symptoms, contact your vet or a pet poison helpline immediately. Full disclaimer.