Egyptian President Abdel Fattah al-Sisi has named a new armed forces chief of staff, the presidency said in a brief statement on Saturday.
He appointed former defence ministry secretary general Mohammed Farid Hegazy to the post, it said, without giving a reason for the change.
His predecessor Mahmoud Hegazy, who had held the post since March 2014, was named a presidential adviser.
The interior ministry on Saturday also announced changes in key security positions, both nationally and in Giza province.
On October 20, the province was the scene of an attack that claimed the lives of at least 16 police officers in the Western Desert, some 200km southwest of Cairo.
Linked to Sisi through the marriage of their respective children, Mahmoud Hegazy recently returned from Washington where military chiefs had gathered to discuss fighting "terrorism".
Mohammed Farid Hegazy's appointment is a major change in the military establishment.
Sisi came to power after the 2013 ouster of Islamist president Mohamed Morsi, for whom he had served as defence minister.
The country's armed forces have since faced an Islamist insurgency including by the Islamic State group, killing hundreds of policemen and soldiers.
The insurgency is concentrated on North Sinai province, although IS has also extended its presence to southern Egypt and the Nile Delta, north of the capital.