Lee's visit to the southern French city of Cannes for this year's G-20 summit was part of a two-nation trip that also took him to Russia's second-largest city of Saint Petersburg earlier this week for summit talks with Russian President Dmitry Medvedev.
Lee attended the two-day G-20 summit as head of one of the "troika" countries, which refers to the previous, current and next hosts of the global economic forum. South Korea hosted a G-20 summit in November last year.
The summit came amid jitters over the possible spillover of the eurozone debt crisis to the world economy.