The goal of our study was to investigate the effects of thinning intensities on carbon (C) storage of soil and forest floor in Quercus spp. stands of Gangwon Province, Korea. Two study stands were located in Yangyang, Gangwon Province (stand I: 45-year-old, stand II: 50-year-old) and these stands were thinned in 2010. Each stand had three plots with different thinning intensities based on stand density: stand I (no thinning, Ct: 0%, light thinning, L: 4%, heavy thinning, H: 25%), stand II (no thinning, Ct: 0%, light thinning, L: 15%, heavy thinning, H: 35%). We measured the C storage of soil at 0-50 cm depth and that of forest floor in 2010. C storages of soil and forest floor were not significantly different among plots with three thinning intensities in stand I (Ct: 53.4 Mg C ha^-1, L: 66.4 Mg C ha^-1, H: 44.9 Mg C ha^-1). On the other hand, forest floor C storage in H plot (6.9 Mg C ha^-1) was higher than that in Ct plot (4.5 Mg C ha^-1). In stand II, C storages of soil and forest floor in thinned plots (L: 85.6 Mg C ha^-1, H: 74.6 Mg C ha^-1) were higher than those in Ct plot (58.7 Mg C ha^-1). Initial effects of thinning intensities on C storage were analyzed as a part of ten-year study, and we expect to determine thinning intensity that can optimize C storage of soil and forest floor by long-term monitoring of changes in C storage at this experimental site.