The event, themed "Asian Youth! Wake up! The Glory of the Martyrs Shines of You", is hosted by one of Asia's fastest growing and devout Catholic communities and will feature a guest appearance from Pope Francis himself on the third day of the event.
The Holy Father will also preside over the closing Mass on Sunday at Haemieupseong Fortress.
Seoul Cardinal, Andrew Yeom Soo-jung, has said that the Pope's visit will 'inject hope' and 'usher in a new era' for the Church in Asia.
Around 6000 Catholics took part in day one of the event on Wednesday - an Opening Mass in Solomoe Shrine, the birthplace of the first Korean priest and martyr, St. Andrew Kim Daegon.
Upcoming activities include prayer, sharing, lectures, workshops and festivals.
Despite its long history, the South Korean Catholic Church was not established until the 18th century.
During his trip, the Pope is also expected to preside the beatification ceremony for 124 Korean martyrs who were victims of religious persecution.
The last papal visit to an Asian country was 15 years ago, when John Paul II travelled to India.