The Norrköping District Court ruled that a woman must pay 1,000 kronor ($155) for slapping the man across the face.
The woman claimed that her violent response came after the man pinched her bottom, something he denies.
The man, who claimed that he was left dizzy after sustaining the blow, was an acquaintance of the woman, reported the Norrköping Tidning.
The court ruled that being pinched on the behind does not constitute an emergency situation and does not warrant a slap, and fined the woman and convicted her of assault.
This incident was not the first of its kind in Sweden. In March last year, a woman in southern Sweden was convicted of assault after slapping a nightclub bottom grabber so hard that she broke his nose. She was fined almost twice as much as the Norrköping woman.