The midfielder spent last season on loan at Sunderland and was a target for Aston Villa this summer but has opted to remain at the Liberty Stadium and fight for his place
The South Korea international, who featured at the World Cup, returns to the Liberty Stadium after spending the previous campaign at fellow Premier League side Sunderland.
The 25-year-old recognises the competition for a starting berth - which has been heightened since the signing of Gylfi Sigurdsson from Tottenham - but is confident he can be a valuable asset to the team.
"It's good to be back. After the World Cup I had three weeks off before I joined up with the team," he told the club' official website. "Now I want to get as fit as I can so I can prove myself in the team.
"It was a very good time for me at Sunderland. I showed that I can help the team, so I hope to do that at Swansea [too].
"There is always competition for a position here - that goes for every player. If you play well then you will play, if not you will be on the bench or not involved, but I will push myself as hard as I can.
"Everyone in this team has great quality. Every season Swansea get stronger and stronger. With the mix of new players along with the players here last year, it will be a good balance."