We conducted leaf decomposition experiment in temperature and CO2 controlled chambers. There are six chambers that have different atmospheric condition; control (as same atmospheric condition as outside of the chamber; B1), control + 3 degrees C; A1, control ×1.4 CO2 concentration; B2, control × 1.8 CO2 concentration; B3, interaction of temperature and CO2 (+ 3 degrees C and ×1.4 CO2; A2, + 3 degrees C and ×1.8 CO2; A3). Oak (Quercus glauca) was planted and has growing in these chambers for seven years. We collected oak leaf litter in each chamber. The leaves were dried, weighed and put in litter bags with 10 mm mesh size. They were placed on the ground of each chamber. The litter bags were collected four times. After collection, leaves were analyzed. High temperature seems restrict fungal propagation but accelerates bacterial colonization. Leaves were decomposed faster in control than high temperature treatment. Water contents of the leaves were highest in high CO2 concentration chambers, followed in control and lowest in high temperature chambers. CN ratio increased with higher CO2 concentration but was not affected by temperature. Regardless of the higher bacterial density, their contribution to leaf decomposition was little during the experimental period.