At this study, the monitoring network of water quality was established in the agricultural watershed an area 14,960 ha of the central southwest of Korea. Loads of nitrogen and phosphorus by agricultural land use were quantified bases on total amounts of stream flow. The land were used as a lowland paddy, an upland and a forest about 12.14 % (1,815 ha), 5.17 % (773 ha) and 80.31 % (12,015 ha) of the area, respectively. For six months, from May 1 to October 31, 1999, the total precipitation was 970 mm and the total amount of stream flow was $80,281,000;m^3$. In the load of agricultural non-point sources relevant to land use, total-N was 138,413 kg, then ammonia-N 13,362 kg, nitrate-N 124,629 kg, and total-P 157 kg. The loss of nutrient which from application of chemical fertilizer were 38.0% in nitrogen and 0.1% in phosphorus to input chemical fertilizer in the watershed.