In Luanda, Mrs Clinton signed a memorandum of understanding with American oil giant Chevron and the US Agency for International Development (USAid) to promote investment in Angola's agricultural sectors like coffee and bananas.
Asked about China's growing influence in Angola, Mrs Clinton said she was not interested in what other people were doing in Angola because her focus was on what the US was doing.
Last year, Angola overtook Saudi Arabia as China's leading source of crude oil.
The US gets about 7% of its oil from the southern African country.
On Monday, Mrs Clinton is expected to hold talks with Angolan President Jose Eduardo dos Santos before leaving for the Democratic Republic of Congo.
Mrs Clinton travelled to Angola from South Africa, where she held talks with President Jacob Zuma in Durban.
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