26 November 2015 Last updated at 01:11 GMT
She says: "We are running a huge campaign in Africa right now about child marriage. It's something we are dead against in every country as we don't think children should be wives.
"Girls should be at school -  they should be able to get skills and a profession to look after themselves," added Ms Dlamini-Zuma.
But she said attitudes tend to take a long time to change. Ms Dlamini-Zuma spoke to the BBC's Zeinab Badawi.
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Chair of the African Union Nkosazana Dlamini-Zuma says marriage can "oppress women".