Yes, Peace Lily is toxic to dogs!
Dogs accidentally consuming the Peace Lily plants can show the following clinical symptoms: Vomiting, Prolonged Depression, Incoordination, Hypersalivaton, Sleepiness Or Excitation, Dilated Pupils, Low Body Temperature, Low Blood Pressure, Coma, Seizure And Death (In Rare Cases).
Peace Lily consumption is also toxic to Cats.
Toxic Principles Of Peace Lily: Insoluble calcium oxalates.
More Info About The Peace Lily Plant
Scientific Name: Spathiphyllum
Family: Araceae.
Also known as: Mauna Loa Peace Lily.
The answer is based on information found on The American Society for the Prevention of Cruelty to Animals (ASPCA) website.