AU chairman and President of Benin Thomas Yayi Boni wished Dlamini-Zuma “great success” at the inauguration ceremony in the Ethiopian capital.
Dlamini-Zuma — who was home affairs minister until a few days ago and is the ex-wife of President Jacob Zuma — beat the incumbent, Jean Ping of Gabon, in a close election in July.
Some observers had feared that her appointment would create divisions between French and English speaking countries on the continent but she has insisted that she would work with all parties.
A doctor by training and a veteran of the fight against apartheid, Dlamini-Zuma, 63, has also served as health and foreign minister.