Abstract. Forests play an important role in the global carbon (C) cycle, and the South Korean forests also contribute to this global C cycle. While the South Korean forest ecosystem was almost completely destroyed by exploitation and the Korean War, it has successfully recovered because of national-scale reforestation programs since 1973. There have been several studies on the estimation of C stocks and balances in the South Korean forests over the past decades. However, a retrospective long-term study including biomass and dead organic matter (DOM) C and validating DOM C is still insufficient. Accordingly, we estimated the C stocks and balances of both biomass and DOM C during 1954–2012 using a~process-based model, the Korean Forest Soil Carbon model, and the 5th Korean National Forest Inventory (NFI) report. Validation processes were also conducted based on the 5th NFI and statistical data. Simulation results showed that the biomass C stocks increased from 36.4 to 440.4 Tg C and sequestered C at a rate of 7.0 Tg C yr−1 during 1954–2012. The DOM C stocks increased from 386.0 to 463.1 Tg C and sequestered C at a rate of 1.3 Tg C yr−1 during the same period. The estimates of biomass and DOM C stocks agreed well with observed C stock data. The annual net biome production (NBP) during 1954–2012 was 141.3 g C m−2 yr−1, which increased from −8.8 to 436.6 g C m−2 yr−1 in 1955 and 2012, respectively. Compared to forests in other countries and global forests, the annual C sink rate of South Korean forests was much lower, but the NBP was much higher. Our results could provide the forest C dynamics in South Korean forests before and after the onset of reforestation programs.