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.

25 May 2017 Last updated at 07:00 BST
He met Newsround at the world famous Chelsea Flower Show, where top gardeners show off their best designs and compete for awards.
George is an ambassador for the Royal Horticultural Society, which runs the show, and he even has his own blog.
Watch his video to find out what's so great about gardening.

They feature on the International Impac Dublin Literary Award's 2016 longlist, alongside BBC journalist Kirsty Wark's debut The Legacy of Elizabeth Pringle.
Libraries in 118 cities around the world nominated 160 books.
The 100,000 euro (Â£71,300) prize winner will be announced on 9 June 2016.
Other British nominees include this year's Bailey's Women's Prize for Fiction winner, How To Be Both by Ali Smith.
The Miniaturist by Jessie Burton, The Bone Clocks by David Mitchell, Caitlin Moran's novel How to Build a Girl and David Nicholl's Us are also on the longlist.
This year it includes 53 novels in translation with works by 44 American, 10 Canadian, 10 Australian, seven Irish, six German and three South African authors.
Past winner Colm Toibin from Ireland is nominated again for Nora Webster, while another former winner, Norwegian Per Petterson, is on the list for Out Stealing Horses.
"Reading groups worldwide each year anticipate the longlist and later the shortlist with excitement and interest," said Dublin city librarian Margaret Hayes.
"From previous experience we know that the 21st winning title will be top of the library readers list for 2016 at home and abroad, bringing readers together in an unparalleled international book club."
Jim Crace won the prize last year for his novel Harvest, while Irish author Kevin Barry won for his debut novel, City of Bohane, in 2013.
This year's Man Booker Prize-winner, A Brief History of Seven Killings by Marlon James, and the winner of the 2014 Governor General's Award for Fiction, The Back of the Turtle by Thomas King, are also nominated.
The full list of British titles in the running:

The motorist received a Â£100 fine and three points on their licence.
Dorset Police said when the driver was stopped he said: "I was trying to find that new Sam Smith song on You tube because I didn't have it on my phone."
The singer has released the song Writing's On The Wall as the theme to the new James Bond film Spectre.
Officers were carrying out checks on traffic offences on Thursday and stopped vehicles which had no insurance as well as others breaking the speed limit.
Spectre sees Daniel Craig return as British spy James Bond, aka 007, in a globe-trotting blockbuster named after a sinister criminal syndicate.
Two-time Oscar winner Christoph Waltz, French actress Lea Seydoux and Italy's Monica Bellucci also appear in the 24th official entry in the long-running series.
Two astronauts on board the International Space Station have taken their first spacewalk outside - to do some repairs and maintenance.
[NEXT_CONCEPT]
Meet George - he wants more children like him to get outside and get into gardening.
[NEXT_CONCEPT]
The Silkworm by JK Rowling's pseudonym Robert Galbraith and Ian McEwan's The Children Act are among 25 British novels in the running for the world's richest literary prize.
[NEXT_CONCEPT]
A driver stopped for using his mobile phone told police he was trying to find the new Sam Smith song on YouTube.