The attack took place during a Coptic wedding at the Virgin Mary church in a ramshackle neighborhood on Cairo's outskirts.
Witnesses said the assailants -- one driving the motorcycle and the other firing the shots -- wore masks during their attack. After opening fire the two drove off into the night.
Authorities said an 8-year-old girl was among the dead.
Coptic Christians have become the target of escalating violence following the removal of Islamist President Mohamed Morsi by the army. The military backed interim government has repressed Morsi's followers in the wake of his overthrow.
"We were waiting for our bride to come, and we were very happy," said Maria Helmy Atta, who witnessed the bloody attack.
After no one claimed responsibility for Sunday's shooting, Egypt was condemned for its polarized religions and political leadership. Interim prime minister Hazem Beblawi called the attack a "lowly criminal act" and vowed to find and punish those who carried it out.