The blast hit the bus carrying the policemen to work posts in a village in the northern Nile Delta province of Baheira, some 160 kilometres north of Cairo, Interior Ministry said.
"Two policemen were killed and 24 others were wounded, including two seriously," a health ministry spokesman said.
The security forces have launched a manhunt to nab the attackers.
Egypt has been battling an increasing Islamist insurgency since the 2013 ouster of president Mohamed Morsi, the country's first democratically elected president.
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The insurgency, mainly backed by Egypt's IS affiliate -- - Ansar Beit Al-Maqdis -- which has often attacked the security forces, mostly centred on the Sinai Peninsula, But, of late, it has spread to other parts of the country.
On Thursday, 29 people, including six policemen, died in a car bomb triggered by the IS targeting a police building in Cairo.
The dreaded group has also claimed the July 11 car bomb attack on the Italian consulate in downtown Cairo in which a passerby was killed. The militants say their attack is in retaliation for a police crackdown targeting Morsi supporters.