The effects of warming (+3 °C) and drought (-30% precipitation) on the fine root decomposition of Pinus koraiensis seedlings were examined using a litter bag method. The study site included a full factorial design with two temperature and two precipitation levels, with three replicates. Litter bags containing fine root litter of 2-year-old P. koraiensis seedlings were retrieved after 3, 6, and 12 months of decomposition. After 12 months, the mass loss of fine roots was significantly increased in response to warming (control = 31.1%, warming = 35.9%, drought = 29.2%, and warming plus drought = 35.5%); no change was observed until 6 months. Mass loss was not influenced by drought or by the interaction between warming and drought. Warming increased the nitrogen concentration of fine root litter but decreased the carbon concentration and carbon/nitrogen ratio after 6 and 12 months. This may be because warming stimulated nitrogen immobilization, which reduced the carbon/nitrogen ratio. Therefore, the carbon/nitrogen ratio may be affected by warming prior to changes in the mass loss of fine roots because roots with a low carbon/nitrogen ratio are generally characterized by high available nitrogen for decomposers. These results suggest that climate change (especially warming) may cause rapid decomposition of organic matter.