The aquisition would increase exposure to one of its few businesses outside its home market.
A unit of Britain's Vodafone Plc, [DATA VOD:Vodacom Group Ltd.] is the most popular mobile operator among South Africans but is dwarfed elsewhere on the continent by rival MTN Group.
Vodacom said on Tuesday it would indirectly raise its stake in Vodacom Tanzania to 82.2 percent from 65 percent by buying new shares in the company's minority shareholder.
It will fund the purchase through cash and existing debt facilities.
It said Tanzania had been its most successful sub-Saharan investment. It is the top mobile operator in the east African nation, with 10 million customers.
The company also has a presence in Mozambique, Lesotho, Nigeria and the Democratic Republic of Congo.
Shares of Vodacom were little changed at 121.76 rand at 1452 GMT, compared with a 1.3 percent decline in the benchmark Top-40 index.