The verdict against Mohamed al-Zawahiri, whose brother Ayman al-Zawahiri heads the global jihadist network, was postponed until September 27.
Zawahiri was arrested in August 2013 at the height of a campaign of repression of Islamists in the wake of the army's ouster of the country's Islamist president Mohamed Morsi.
He and 67 co-defendants are accused of having formed "a terrorist group linked to Al-Qaeda" and plotting attacks on government installations, security forces and Egypt's Christian minority -- all charges which his lawyer has denied.
The judge forwarded today's death sentences for consultations to the country's grand mufti, the official interpreter of Islamic law.
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The Al-Qaeda leader's brother is specifically charged with having formed the group, arming its members and arranging training in the manufacture and use of explosives.
Group members allegedly trained at secret camps in districts of Cairo and in the Nile Delta, north of the capital.
Fifty-two accused including Zawahiri are in custody while 13 are on the run and being tried in absentia. The last three are dead, one reportedly in custody.