Mansour had initially announced a month-long state of emergency on August 14, with deadly unrest sweeping Egypt as police dispersed two Islamist protest camps.
“President Adly Mansour decided to extend the state of emergency…by two months,” presidential spokesman Ehab Bedawy said in a statement.
The decision was taken in light of “developments and the security situation in the country,” he said.
More than 1,000 people were killed on August 14 and following days after police dispersed two sit-ins in Cairo by ousted Islamist president Mohamed Morsi’s supporters.
Islamists at the time lashed out at Christians, accused of supporting the military coup which ousted Morsi, and burned down several churches.
Violent protests have largely subsided, giving way to militant attacks such as a suspected suicide bombing that targeted the interior minister last week in a failed assassination bid.