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Soil erosion and muddy runoff from sloping agricultural fields during monsoon season has been a major cause of water quality and aquatic ecosystem degradation in Korea. The objective of this research was to experimentally test the effect of rice straw mats on the reduction of runoff, sediment and discharge under a laboratory scale with different rainfall intensity and slopes. Experimental treatments were three types of rice straw mat, rainfall intensity (30 and 60 mm/h), and slope (10 and 20%). The time of initial runoff from control plots was significantly faster than that from covered plots regardless the cover material, rainfall intensity and slope (Figure 1). Runoff volume and coefficients from covered plots were significantly lower than those from control plots. Under the 30 mm/h and 10% simulations, average runoff coefficient of covered plots decreased more than 92%. Under 60 mm/h and 20% simulations, the ratios were between 39.8~58.1%. Under the condition of 30 mm/h rainfall and 10% slope, sediment discharge from covered plots was practically zero. And at 20% plots, sediment reduction ratio was more than 95%. Under the condition of 60 mm/h rainfall, sediment reduction ratio of 10 and 20 % plots ranged between 86.3~95.3% and between 79.8~ 86.5%, respectively. The differences in initial runoff time, runoff and sediment discharge among different cover materials were not significant. Rainfall intensity showed higher impact on initial runoff time, runoff, and sediment discharge than slope. It was also shown that even if runoff reduction by surface cover were low, sediment discharge reduction could be very significant and contribute to improve the water quality of streams in sloping agricultural regions. It was concluded that the use of straw mat and PAM on sloping agricultural fields could reduce soil erosion and muddy runoff significantly and help improve the water quality and aquatic ecosystem in receiving waters.