The court in Krems, 30 miles west of Vienna, found Blauensteiner, 66, guilty of poisoning Alois Pichler, 77, with fatal doses of medication. The jury reached its verdict at 3am after12 hours of deliberation.
Blauensteiner, in a black suit and cream blouse, remained composed, muttering and looking at her watch impatiently as the verdict was read out. Asked if she understood the sentence she said with defiance: "I understand perfectly".
The jury said Blauensteiner's "pure greed" justified the heavy sentence, noting her "malicious actions did not give the victim any chance to defend himself".
Blauensteiner's former lawyer, Harald Schmidt, was sentenced to seven years in jail for being an accomplice to grievous bodily harm and falsifying Pichler's will. The two have said they may appeal the verdict.
Although Blauensteiner was charged with only one murder, police are investigating other deaths. Blauensteiner is accused of placing advertisements in newspapers to meet rich, elderly men, poisoning her victims and then gambling away the money she was left in their wills.
Blauensteiner said she enjoyed nursing pensioners and it was a coincidence that some of her patients had died.