The US space agency said it would open the orbiting station to tourism and other business ventures.
There will be up to two short private astronaut missions per year, said Robyn Gatens, the deputy director of the ISS.
The first component of the ISS was launched into orbit in 1998, and the station has been continually occupied since November 2000.
It said that private commercial entities would be responsible for determining crew composition and ensuring that the private astronauts meet the medical and training requirements for spaceflight.
The two companies hired by Nasa were Boeing and SpaceX, the Washington Post reported.
Nasa had previously banned any commercial use of the space station and prohibited astronaut’s from taking part in for-profit research.
The new commercial opportunities announced on Friday are part of a trajectory towards full privatisation of the ISS. US President Donald Trump published a budget last year which called for the station to be defunded by the government by 2025.
The space agency recently announced that it planned to return to the moon by 2024, taking the first woman there and the first person in decades.