The alleged incident took place in the 46-year-old man's apartment in November after he and the 21-year-old woman went on a date in Gothenburg, TheLocal.se reported.
The woman told investigators the last thing she remembered from the evening was falling asleep in the man's apartment, fully clothed. She said she woke up the next day, locked in a room, the newspaper Metro reported.
Tests showed the woman's blood-alcohol level was between 2.0 and 2.5 mille -- 10 times greater than the legal limit in Sweden -- putting her in what the Gothenburg District Court called a "particularly vulnerable situation."
However, the man testified he did not know how drunk the woman was, and that she was "active" during sexual activity.
The court ultimately acquitted the man of the rape charges, saying it had not been proven he "understood or was aware that" the woman was drunk and did not want to participate in the sexual activity.
A lawyer for the woman said she plans to appeal the ruling.
"She's very concerned and scared and taken aback by the situation," lawyer Ewa Backman Kihl told Metro.