Mission control said it was "a great landing"
The orbiter was returning from an 11-day mission to expand the International Space Station (ISS).
Atlantis landed on schedule at 1226 local time (1626 GMT), after slowing enough to drop from orbit over the Indian Ocean and then flying the final distance like an aeroplane.
The crew performed four spacewalks during their orbital stay, installing a 13-metre-long (43-feet) girder to the platform which will act as the station's backbone as it continues to grow in the coming years.
The astronauts also tested the first "railroad in space" - a trolley system that runs along the girder, and which will serve as a mobile base for a robotic arm.
More laboratories
Before re-entry, the crew conducted TV interviews during which they assessed their mission's work.
"We made our first step toward our commitment to the international partners," Mike Bloomfield said. Once work on the new girder and the ISS solar arrays is finished, "we will actually have enough power that we can add two more laboratories".
Japan and the European Space Agency are both committed to adding laboratory modules to the platform.
Atlantis crew member Jerry Ross reflected on his trip into space - a record seventh launch from Earth.
"I felt the same on this one as I did on the first one - totally enthralled. The spacewalks were indescribable," he said.
The space station's current three-member crew still has two months left in its six-month tour of duty.