In order to study the long-term change of water quality, water analysis for 9 items was conducted at 13 sites surrounding the Kumho river system for 18 times from September 1993 to August 1999. Analytical items for the study of water quality are as follows; water temperature, pH, BOD, COD, DO, SS, electrical conductivity, oil and grease, ABS and phenol. The six year term was divided into Part I(second study) and Part Ⅱ(third study), which covers the term from September 1993 to August 1996 and the term from September 1996 to August 1999, respectively. The mean values obtained for three years for water temperature, pH, BOD, COD, DO, SS, electrical conductivity, oil and grease, ABS and phenol for the Part I period showed 18.4$^{circ}C$, 7.9, 4.88 ppm, 9.66 ppm, 9.0 ppm, 618.0 $mu extrm{m}$ho/cm, 6.9 ppm, 2.63 ppm, 3.57 ppm and 0.98 ppm, respectively. The mean values obtained for water temperature, pH, BOD, COD, DO, SS, electrical conductivity, oil and grease, ABS and phenol for the Part Ⅱ period showed 18.0$^{circ}C$, 8.0, 2.86 ppm, 7.40 ppm, 8.94 ppm, 541.0 $mu extrm{m}$ho/cm, 6.0 ppm, 5.43 ppm, 0.94 ppm and 0.01 ppm respectively. The values of BOD, COD, SS, electrical conductivity, ABS and phenol in the second period were found to be decreased by $1}$1.71, $1}$1.31, $1}$4.15, $1}$3.80 and $1}$98, respectively. The values of water temperature, pH and DO were nearly constant. However, the concentrations of oil and grease were found to be increased about 2.06 times in the second period.