"A little more than one hour into Tuesday's spacewalk, Luca Parmitano of the European Space Agency reported water floating behind his head inside his helmet," reported Xinhua citing NASA in a statement.
"The water was not an immediate health hazard for Parmitano, but Mission Control decided to end the spacewalk early."
The statement said Chris Cassidy of NASA and Parmitano were already safely back in the space station, and engineers were continuing to evaluate data to determine the cause of the leak.
Both astronauts had planned to lay wires for the arrival of a new Russian Multipurpose Laboratory Module later this year and to do other maintenance works.
The spacewalk officially ended at 1329 GMT, only 1 hour and 32 minutes into the planned 6.5-hour venture outside the space station, making it the second shortest in the orbital laboratory's history.
NASA said none of those tasks were urgent, and that the crew and station were not in any danger.