28 October 2015 Last updated at 14:19 GMT
Scott Kelly and Kjell Lindgren had to grease the station's big robot arm, re-route some cables and remove some insulation.
The spacewalk had to be delayed after Lindgren switched on the water flow in his suit too soon.
Mission Control had to make sure the suit would be safe, before they gave the all-clear.
Water is needed to cool the suit.
Kelly who's been living at the orbiting lab since March will stay until March 2016.
But early on Thursday morning this week, he will break the American record for NASA's longest single space shot.
That 215-day record - more than seven months - was set in 2007.
President Barack Obama already has sent his congratulations in a phone call last week- telling him his time in space is  ``nothing to sneeze at.''
Kelly replied ''It shouldn't be a problem getting to the end with enough energy and enthusiasm to complete the job. Records are made to be broken.''
Earlier this month, Kelly broke the U.S. record for the most time in space: 383 days and counting over four missions. It will be 522 days in total by the time he returns to Earth.
The pair will do a second spacewalk on Nov 6th.
Two astronauts on board the International Space Station have taken their first spacewalk outside - to do some repairs and maintenance.