Cosmonauts Fyodor Yurchikhin and Alexander Misurkin conducted extravehicular activities in preparation for the addition of a new Russian module to the ISS later this year, RIA Novosti reported.
Russian's Roscosmos is expected to launch a new research facility, airlock and docking port late in 2013.
The cosmonauts also replaced an aging fluid flow control panel on the station's Zarya module as preventative maintenance on the cooling system for the station's Russian segment, and retrieved two science experiments.
The space walk was Misurkin's first; Yurchikhin has made six.
It was the second of up to six Russian spacewalks planned for this year, NASA reported.