We used growth chamber incubation to investigate the physiological characteristics of water in the soil of Pinus koraiensis seedlings at two levels of CO2, i.e. at 700 and 350 μmol/mol. The results revealed the following: 1) Starting from the same initial level of soil moisture, at the higher CO2 concentration, the soil moisture was higher after five days under similar growing conditions. 2) An elevated CO2 level resulted in a decrease of stomatal conductance, in the rate of transpiration and in the amount of water in the aboveground parts of the seedlings, but led to an increase in water use efficiency and leaf water potential, while soil moisture did not differ greatly in the two CO2 treatments. 3) While soil moisture differed in the two CO2 treatments, at 700 μmol/mol CO2 there were no significant changes in stomatal conductance, the rate of transpiration, water use efficiency and leaf water potential. At 350 μmol/mol CO2 stomatal conductance and the rate of transpiration decreased, while the increases in water use efficiency and leaf water potential were not significant.