The 54-year-old politician was indicted in April on charges of forcing his former secretary, Kim Ji-eun, to have sex with him four times and molesting her multiple times between the middle of last year and early this year in Seoul and while on overseas business trips.
The Seoul Western District Court said that there is not sufficient evidence to prove An used his position to have sexual relations with the plaintiff.
It also did not accept the victim's argument that he had physically subdued her so that she was unable to resist.
The court decision has sparked a harsh backlash in the society.
