The Arizona Democrat remained in critical condition, Politico reported. Doctors at University Medical Center said they took her off the ventilator and carried out an operation allowing her to breathe without it.
Giffords was shot in the head, six people were killed and 12 others were wounded last Saturday at an event she was holding outside a Tucson supermarket.
Without the breathing tube, Giffords will be able to talk, doctors said. That will allow them to make a preliminary assessment of the damage done by the bullet that went through her brain.
"We couldn't have hoped for any better improvement than we are seeing now given the severity of her injury," said Dr. Michael Lemole, a neurosurgeon on the team treating the congresswoman.
Giffords has passed such marks as moving her hands and arms, opening her eyes, responding to commands, sitting up in bed and lifting her legs.
She also has been breathing on her own, but the breathing tube had been kept in to prevent fluid in her lungs that could progress to pneumonia. With the removal of the tube, she can be moved from intensive care to a normal ward, where her condition can be downgraded from critical to serious.