final shuttle space walk
Astronauts Mike Fincke and Greg Chamitoff's seven-and-a-half-hour walk completed Nasa's part in constructing the ISS.
The astronauts will return to Earth in a few days on space shuttle Endeavour's last voyage.
One final shuttle is scheduled for July to bring supplies to the ISS.
The BBC's Tom Burridge in Washington says the ISS is now the size of a football field and can house six full-time residents who spend their time conducting scientific experiments and research conditions for possible longer missions, such as travelling to Mars.
Astronaut Chamitoff said before ending the 164th and last shuttle space-walk: "Twelve years of building and 15 countries and now it's the Parthenon in the sky and hopefully the doorstep to our future. So congratulations everybody on assembly complete."
As he attached the final 50ft (15m) boom, he said: "Amazing. Boy, this is a big space station."
Endeavour is scheduled to return to Earth on Wednesday.
It will then be prepared for public display at the California Science Center in Los Angeles.
Russia still plans to carry out space-walks at the ISS, adding at least one more chamber to the structure. Those in the station will also carry out walks as necessary.