His promise to take a bigger bite out of foreign investors' profits, scrap the current constitution and launch a "revolution" for the poor has seen his support swell in the weeks running up to the poll, despite concerns over his lack of a firm policy programme and allegations of human rights violations during his time an army commander.
What do his critics say?
Mr Humala's plans to increase state control over the economy and restrict foreign investment have sent jitters through the financial markets and foreign investors are growing increasingly wary.
And the US is concerned by his many similarities to Venezuela's President Hugo Chavez, who has been seeking to counter US influence in the region.
Like Mr Chavez, Mr Humala has been labelled a populist and a nationalist, and like Mr Chavez he is a fierce opponent of US-style free market policies.
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http://news.bbc.co.uk/go/pr/fr/-/1/hi/world/americas/4879968.stm
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