The boy was put on trial for having downloaded at least 24 films from the internet and then sharing them with others.
He was considered to be the youngest person ever to be put on trial in Sweden for filesharing crimes.
The boy was reported to police by his school principal after the school’s IT department discovered the downloaded films on his computer.
They made the find after having identified the boy’s computer as the source of a virus that had infected the school’s computer system.
While he admitted to downloading the films, the 15-year-old claimed he was unaware that his actions were criminal.
Two lay judges who heard the case believed the boy’s defence, while the head judge and another lay judge were in favour of a conviction, the Göteborgs-Posten (GP) reported.
However, the split among the judges was sufficient for an acquittal.
Ahead of the trial, prosecutor Fredrik Ingblad told The Local he was confident the boy would be convicted. Following the court’s ruling, however, he vowed to appeal the non-guilty verdict.
“I can’t do anything other than appeal. This is an absurd ruling, quite simply,” he told the TT news agency.
The trial, which gained wide attention in the Swedish press because of the defendant’s young age, was also watched closely by the Pirate Party, a political party which wants to see reforms of copyright laws.
“I can only imagine how it must feel to be a 15-year-old who is dragged into court for doing one of the greatest things one can do, sharing culture,” Pirate Party leader Anna Troberg said in a statement.