Speaking at the firm's interim results presentation on Thursday, Eskom chairman Zola Tsotsi said Mr Dames was stepping down for "personal reasons" and that a search for his successor was underway.
Mr Dames was appointed CEO on 1 July 2010 and resigns as Eskom announced profit fell 3.2 percent amid higher production costs and constrained supply.
Profit after tax declined to R12.2 billion in the six months ended September from R12.6 billion a year earlier, the company said.
Eskom last month declared emergency measures to avoid outages with the utility struggling to match demand.
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