SpaceShipTwo was carried aloft by its mothership to an altitude of 45,000ft and released over the Mojave Desert.
After the separation, SpaceShipTwo, manned by two pilots, flew freely for 11 minutes before landing at an airport runway followed by the mothership.
* Six-passenger aircraft glides smoothly to Earth after disconnection from mothership at 45,000ft
* Virgin Galactic boss delighted with 25-minute 'flight'
The entire test flight lasted about 25 minutes.
'It flew beautifully,' said Virgin Galactic chief executive George Whitesides.
The six-passenger SpaceShipTwo is undergoing rigorous testing before it can carry tourists to space. In the latest test, SpaceShipTwo did not fire its rocket engine to climb to space.
Until now, SpaceShipTwo has flown attached to the wing of its special jet-powered mothership dubbed WhiteKnightTwo. Sunday was the first time the spaceship flew on its own.
Virgin president Sir Richard Branson said: 'It's a very big deal. There are a number of big deals on the way to getting commercial space travel becoming a reality. This was a very big step.
'We now know that the spaceship glides. We know it can be dropped safely from the mothership and we know it can land safely. That's three big ticks.'
SpaceShipTwo will make a series of additional glide flights before rocketing to space.
Sir Richard added: 'The next big step will be the rocket tests actually on the spacecraft itself.
'We've obviously have done thousands of rocket tests on the ground, the next big test is in the air. We'll be doing gentle rocket tests in the air, ultimately culminating into taking the spaceship into space.'
SpaceShipTwo, built by famed aircraft designer Burt Rutan, is based on a prototype that won a $10million (£6.3million) prize in 2004 for being the first manned private rocket to reach space.
Tickets to ride aboard SpaceShipTwo cost $200,000 (£125,000). Some 370 customers have plunked down deposits totaling $50million (£31.3million), according to Virgin Galactic.
Commercial flights will fly out of New Mexico where a spaceport is under construction.
Officials from Virgin Galactic and other dignitaries will gather at the spaceport on October 22 for an event commemorating the finished runway. The event will also feature a flyover by SpaceShipTwo and WhiteKnightTwo.
