The elderly patient's right leg was removed instead of his left, with the mistake only discovered two days later.
On Wednesday, the court in Linz found the 43-year-old guilty of gross negligence and fined her €2,700 (£2,296).
The widow of the patient, who died before the case came to court, was also awarded €5,000 in damages.
The patient attended the clinic in Freistadt last May to have his leg amputated but the surgeon marked the wrong limb for amputation, AFP news agency reports.
The mistake was identified during a routine bandage change and the patient was told he would have to have his other leg amputated as well.