Polls are open from 8 am to 7 pm (0600-1700 GMT) through the length and breadth of the country.
Analysts see it as a major step forward for Egypt and expect high turnouts as the referendum could go a long way to restore faith in elections. However, the referendum in itself has divided opinions wherein a segement of the population prefer amendments in the constitution as opposed to some other who want it to be completely rehashed.
The Muslim Brotherhood, Egypt's biggest organised opposition group support the amendments while other opposition parties and reformists, including prospective presidential candidates Mohamed ElBaradei and Amir Moussa, oppose them.
More than 45 million Egyptians are expected to cast their votes.
The military council which forced Mubarak to step down hopes the changes are approved by the people of Egypt thus enabling it to hold parliamentary and presidential polls and cede power to an elected government within months.
Hosni Mubarak was forced to hand over power to the army following 18 days of protest by the entire country. The then vice-president Omar Suleiman had announced that a military council would run the affairs of the most populous Arab nation, until a new democratically elected government assumes power.