The pair had allowed the brother of a terminally ill, paralysed patient to turn off his breathing apparatus in May 2004 and one of the defendants administered strong painkillers. The man, Timothy Sanders, died minutes later.
The former head of neurology at the rehabilitation centre in the eastern city of Magdeburg, Paul Schoenle, had been accused of manslaughter. The other doctor, ward physician Frantisek Kovacic, was tried on charges of accessory to manslaughter and grievous bodily harm for ignoring warning alerts from the patient's room and administering the painkillers without medical grounds.
"The court found that the doctors behaved correctly both ethically and medically," a court spokeswoman said, adding that the judges had determined that Sanders's condition was already terminal when his life was ended.
The British man had been paralysed since an accident in 2002 and was unable to breathe unaided. The following year, Sanders was transferred to the rehabilitation centre in Magdeburg where his condition worsened. He could barely speak and regained consciousness only for brief periods of time.
Sanders's brother Paul turned off the patient's breathing apparatus in May 2004 "with the knowledge of the chief doctor and the ward physician" and the consent of the rest of the family, prosecutors said.
Non-active euthanasia - such as switching off hospital equipment - is not illegal in Germany if the patient gives his or her consent, or if it can be proven that the patient instructed relatives to allow doctors to stop treatment.
However, the country has been swept up in a debate about assisted suicide in which people who are not fatally ill seek to die with help from another, a practice that is illegal in Germany but has grown more frequent in recent years.