Cairo - An explosion inside Cairo's Coptic cathedral killed at least 20 people and injured 35, Egypt's state television said.
There was no immediate claim of responsibility.
On Friday, two roadside bombs - one in Cairo and one north of the capital - killed six policemen and wounded six others.
Egyptian security forces are fighting an Islamist insurgency led by Islamic State's branch in North Sinai, where hundreds of soldiers and police have been killed.
The insurgents have also launched deadly attacks Cairo and other cities.