The two leaders reached the agreement in summit talks in Seoul, pledging to work closely together to bolster trade and investment between the two mutually supplementary economies as the Southeast Asian nation pursues reform and openness, the presidential office said in a statement.
Thein Sein arrived in Seoul on Monday for a three-day state visit. His trip follows Lee's landmark visit in May to the Southeast Asian nation that has been emerging from international isolation with sweeping democratic reforms since Thein Sein took power last year after decades of military rule.
Democratic reforms have made Myanmar an attractive destination for investment. About three times the size of the Korean Peninsula, the country has one of the world's largest natural gas reserves and big deposits of iron ore, zinc, nickel and other mineral resources.
Myanmar is also considered a strategic foothold linking huge markets in nearby China and India. Though one of the world's poorest nations, with an annual per capita income of US$700, Myanmar has a high literacy rate and could provide cheap, quality labor for companies.
Lee and Thein Sein also agreed to continue cooperation in existing gas development and power plant projects in Myanmar and work actively together to boost cooperation in energy and resources development, infrastructure and construction, the office said.
The two sides also signed a framework agreement on grant aid. South Korea also agreed to seek projects to share its economic development experience with Myanmar and signed a memorandum of understanding calling for cooperation in Myanmar's efforts to establish a state research think tank on economic development.