Any person born outside the United Republic of Tanzania on or after Union day is deemed to be a citizen of the United Republic by descent if one of his parents is a citizen of the United Republic of Tanzania by birth or naturalization.
The law provides that any individual who is born from parents of different nationality shall prior to obtaining the age of eighteen renounce the other country’s citizenship to acquire or remain with only the Tanzanian citizenship, as stated in section 7. (1) of the Citizenship Act which provides that,
 “Any person who, upon the attainment of the age of eighteen years, is a citizen of the United Republic or was a citizen of the former Republic of Tanganyika or of the former People’s Republic of Zanzibar and also is or was a citizen of some country other than the United Republic or either the former Republic of Tanganyika or the former People’s Republic of Zanzibar shall, subject to the provisions of subsection (8), be deemed to have ceased to be a citizen of the United Republic (Cessation of dual citizenship) upon the specified date unless he previously renounced his citizenship of that other country, taken an oath of allegiance and, in the case of a citizen by descent, made and registered the declaration prescribed by Parliament regarding his intention as to residence.”
If an individual wishes to retain his/her Tanzanian citizenship, then they must make an application for renunciation of their other citizenship at the embassy of the other country (the country where he was born) where they shall be required to fill in forms and state that they intend to cease being a citizen of that country. Then the individual shall be required to visit the Tanzanian immigration and  take an oath of allegiance to Tanzania and, register the declaration of citizenship as prescribed by Parliament regarding his intentions.
However, if the individual is above the age of 21 and had not taken any measures to renounce his citizenship before then the law prescribes that there is an automatic revocation of his Tanzanian citizenship and thus if he/she wishes to acquire Tanzanian citizenship then he/she shall have to make an application for Tanzania citizenship by naturalization to the Minister responsible for citizenship matters.
The renunciation fees charged shall be subject to the fees and rates of the embassy concerned. However, if the individual does not renounce his foreign citizenship, then the law regards him as a foreigner and thus the individual must apply for citizenship by naturalization.