In forested areas, as rainfall passes through the canopy layer, the particle size and falling speed change, resulting in throughfall exhibiting different physical properties from gross rainfall(i.e., rain outside the forest). Since these characteristics can influence soil erosion processes in forests, it is necessary to understand throughfall dynamics. This study compared and analyzed the drop size distribution (DSD) and kinetic energy (KE) of raindrops in throughfall and gross rainfall using data from optical disdrometers. The disdrometers were installed at three locations on the Chuncheon campus of Kangwon National University: a Korean pine (Pinus koraiensis, FPk) stand, an oak stand (Quercus spp., FQ), and an open space (OP) to collect data. The analysis results showed that the median volume diameter (D50, average ± standard deviation) was greater in throughfall across all forest stands compared to gross rainfall (OP: 1.98±0.76 mm), with values in the following order: leafed period FQ (FQL, 4.20±0.61 mm) > FPk (3.68±1.04 mm) > leaf-fall period FQ (FQLF, 2.32±0.45 mm). The volume ratio of raindrops in each drop diameter class indicated that throughfall in all forest stands had higher proportions of drops approximately 3.0–3.5 mm and larger, compared to open-area rainfall. Rainfall KE showed a similar pattern to the drop size distribution, with higher values under comparable rainfall intensities in the following order: FQL > FPk > FQLF > OP. These results suggest that throughfall exhibits a DSD distinct from that of gross rainfall, likely due to scattering and accumulation on leaves and branches, which may increase the amount of KE transmitted to the forest floor. Accordingly, a comprehensive understanding of throughfall DSD in relation to forest stand structure is important for improving the accuracy of soil erosion predictions in forested ecosystems.