At the same time the 500,000 Zanzibari voters will cast a second ballot to elect a parliament and president for the islands.
Tanzanians go to the polls on Sunday in the first post-independence election which has not taken place under the shadow of founding president Julius Nyerere.
More than 10 million people have registered to vote to choose a 231-seat parliament, local government leaders and a president for the union of Tanzania, which consists of the mainland and the semi-autonomous islands of Zanzibar.
At the same time the 500,000 Zanzibari voters will cast a second ballot to elect a parliament and president for the islands.
Impoverished for decades under Julius Nyerere, the first president who pursued a socialist programme after the country's 1961 independence, Tanzania has recently been praised for its economic reforms.
The country is also seen as a bastion of stability and calm in a region where ethnic conflicts often reign. There are some 120 different tribes but a marked lack of tribal tensions.
President Benjamin Mkapa, a former schoolteacher, and the leader of the ruling CCM (Chama Cha Mapinduzi) party, appears confident of winning a second term.
In the last elections in 1995 he enjoyed the personal endorsement of Julius Nyerere. For the first time following Mr Nyerere's death last year, he is standing outside his mentor's shadow.
But he thinks that his Western-led economic reforms, which have seen the privatisation of many public companies, and increased foreign investment, will carry him to victory.
Opposition split
Political analysts say that President Mkapa will also be helped by the fact that the opposition is split. There are three opposition presidential candidates.
Challenges
The winner of the election will continue to face enormous problems and challenges. While Tanzania's gold and mineral reserves, its vast arable lands and its gameparks and other tourist attractions have yet to be fully developed, the country continues to be burdened by a bureaucracy full of corruption.
The main coastal city of Dar es Salaam boasts cyber cafes and a proliferation of mobile phones, but between 15 and 18 million Tanzanians - roughly half of the population - live below the World Bank poverty line of 65 US cents per day. Education and health services are in crisis.
Zanzibar tensions
On Zanzibar, the CCM presidential candidate, Aman Abeid Karume, could face a stiff challenge from the opposition CUF candidate Seif Shariff Hamad.
The CUF maintains that the CCM only won the last elections because it rigged the vote - a view broadly supported by Western donors which suspended funds.
Human rights groups have also criticised the CCM for the detention of 18 opposition figures on charges of treason. It's on the Indian Ocean islands that tensions could flare on election day.