The 34-year-old singer, whose real name is Park Jae-Sang, rocketed to international fame after "Gangnam Style", a techno ode to a trendy Seoul neighbourhood, become a worldwide hit following its debut in July.
The video went viral online with its goofy signature horse-riding dance and on Friday ousted singer Jennifer Lopez's dance hit "On the Floor" from second place. But it still trails behind Canadian teenage heartthrob Justin Bieber's "Baby", which has had over 795 million hits.
John Hirai, head of music at YouTube's Korea-Japan branch, told a conference in Seoul that Psy would pass Bieber on YouTube's most-watched list in about a month.
He thinks the secret of Psy's success lies in the speed at which the singer uploaded a sequel video on his official website, as well as footage of the making of his video and interviews, for users wanting to know more about him and "Gangnam Style".
"It comes like a total package at the end, so it just generated views," Hirai said, according to Yonhap news agency. "I've been in this music business for 25 plus years and I've never seen anything like this and I've never imagined anything like this would come out of Asia. It's just unbelievable but it's overwhelming," he said.
Psy has also remained at number two on the Billboard Hot 100 music chart in the United States for a sixth straight week after topping charts in countries including Britain and Australia.