He called an agreement signed in January to develop the largest uranium mine in Africa a "win-win" for both Niger and France.
"Obviously we're here because we need your uranium but we're also here because we need strategic partners and Niger is a strategic partner that is absolutely essential," Sarkozy said.
The former French colony is a major source of uranium for Areva.
French mining operations have not been without controversy, as local and international campaigners accuse Areva of looting Niger's natural resources.
They have also criticised the "catastrophic" effects of the the activities on the environment, and thousands of Tuareg nomads have been displaced to make way for the mines.
The Tuareg, seeing little benefits from the mineral extraction, have reacted violently, launching attacks against government troops and mining facilities.
There have been reports that Areva is demanding that the French government assist Niger's army to fight the Tuareg.
During Sarkozy's DRC leg of the trip, Areva signed an agreement with the Kinshasa government allowing the company to prospect for and mine uranium.
Historically the DRC has produced significant quantities of uranium.
However, Sarkozy also spent a large part of his time in Kinshasa addressing regional political issues, describing the country as the "backbone" of central Africa.
He praised the government for letting troops from neighbouring Rwanda and Uganda into the country to help fight armed groups opposed to the government.
"France will always be by your side to map out the future and to push for peace," Sarkozy said.