The bus, on the way to Kothamangalam from Bison Valley, fell into the gorge at Adimaly area after the driver lost control because of slippery road caused by rains, they said.
The passengers had a miraculous escape as the vehicle got stuck in a tree in the gorge, police said.
Officials of fire department and police rescued the passengers.
Around 25 of them suffered minor injuries in the mishap and were hospitalised in Adimaly, Kothamangalam and Kolencherry, they added.