"AU Commission Chair Dlamini-Zuma didn't submit an application for a second term when the deadline closed yesterday, 31 March," her spokesman Jacob Enoh Eben said.
Her successor to the four-year post will be appointed during the next AU summit, due in July in the Rwandan capital Kigali. The official list of candidates is expected to be revealed later this month.
Dlamini-Zuma, 67, a South African, was the first woman to hold the AU's top job when she was elected in 2012.
An experienced diplomat, a veteran of the fight against apartheid and a doctor by training, she has served as health, interior and foreign minister in South Africa. Her former husband is South African President Jacob Zuma.
More From This Section
Speculation already rife in the the corridors of the AU as to her successor.
Algerian Foreign Minister, and former AU Commissioner for Peace and Security, Ramtane Lamamra, has long been seen a possible candidate.
But SADC countries, the regional organisation in Southern Africa, appear determined to keep the role, pushing the name of Botswana's Foreign Minister, 64-year old Pelonomi Venson-Moitoi. She was a journalist before joining her government's civil service.