Their Dragon capsule – supplied and operated by the private SpaceX company – attached to the bow section of the orbiting lab 422km above China.
After a wait for leak, pressure and temperature checks, the pair disembarked to join the Russian and American crew already on the ISS.
Hurley and Behnken launched from Florida on Saturday.
Theirs is the first crew outing launched from American soil since the retirement of the US space agency (Nasa) shuttles nine years ago.
