Objective of this study was to investigate adsorption characteristics of PO4-P to biochar produced from oak tree in respective to reduce eutrophication from runoff water in cropland. PO4-P concentration was analyzed by UV spectrophotometer. For adsorption experiment, input amount of biochar was varied from 4 to 20 g L-1 with 30 mg L-1 PO4-P solution. Adsorption amounts and removal rates of PO4-P was increased at 33.3% in 4-14 g L-1, and increased at 28.6% in 4-16 g L-1, respectively. Adsorption characteristics of biochar were investigated with application of Langmuir isotherm. The maximum adsorption amount(qm) and binding strength constant(b) were calculated ad 0.1 mg g-1, and 0.1 L mg-1, respectively. The sorption of PO4-P to biochar was fitted well by Langmuir model because it was observed that dimensionless constant(RL) was 0.4. It was indicated that biochar is favorably adsorbed PO4-P because this value lie within 0