The ability of forest watersheds to conserve and regulate water has received much attention recently. Much research has tried using different approaches such as the infiltration capacity, porosity of soil layers, recession-curve-displacement analysis, and water budgets to estimate the water conservation ability of a watershed. However, many factors are involved in the ability to conserve water, and therefore it is difficult to use some physical quantities to give accurate estimations.Baseflow is the discharge of water that drains from deeper subsurface runoff or originates from the groundwater system, and it is the best and more direct index to describe the ability of a watershd to conserve water. This study used the variable-slope baseflow separation method to analyze rainfall events of the Lienhuachih no 5 experimental watershed to estimate the quantiles of conserved water of the target watershed. From results of 46 rainfall event analyses, the average daily baseflow discharge was about 1.164 (range, 0.474~3.265 mmd-1), which is equivalent to 11.64 m3d-1ha-1 or 4284 tonsha-1yr-1 and accounts for 21% of annual rainfall. Combining the estimated baseflow amount and temporal rainfall distribution can give a more-reliable estimate of the ability of a forested watershed to conserve water.