Hannuri, a local law firm which represents the users, filed the class action lawsuit with the Seoul Central District Court against Apple and Apple Korea, the local unit of the iPhone manufacturer, reports Xinhua news agency.
The iPhone customers demanded the damages worth KRW 200,000 ($188) per plaintiff, or KRW 12.75 billion ($12 million) in total.
It was the country's biggest-ever class action suit in history.
Around 400,000 iPhone customers originally sought to join the legal action, but the number fell in the course of verifying identification and offering necessary documents, according to the report.
Apple was accused of slowing down old iPhones through software tweak to make users buy new ones once a new model is released.
The iPhone maker claimed that its software intentionally slowed some models under certain circumstances to protect them from automatically shutting down.
Hannuri said that though Apple recognized the underperformance of iPhones via iOS upgrade, it covered up the truth in offering the software to hide faulty battery, prevent customer secession and promote the sale of new models.
Civic group activists, which represent 122 and 401 iPhone users each, filed their respective class action suits against Apple and Apple Korea in mid-January and early March for damages worth KRW 2.2 million ($2,070) per person.