In order to reveal the relationship between the concentration of chlorophyll- a and the environmental factors affecting eutrophication, the present study was biweekly conducted at G stations in the lower part of the Han river during the period from Feb. 24,2001 to Feb. 9,2002. Water temperature was changed from $0.5^{circ}C$ to $26.4^{circ}C$, pH was 5.77${sim}$8.99, DO 3.15${sim}$14,36 mg $L^{-1}$, BOD 0.90${sim}$7.45 mg $L^{-1}$, and COD 1.16${sim}$9.13 mg $L^{-1}$. TN and TP were ranged from 1.68${sim}$20.96 mg $L^{-1}$, and 0.02 ${sim}$ 1.17 mg $L^{-1}$, respectively. $NH_4;^+$-N, $NO_3;^-$-N, and $PO_4;^{3-}$-P were ranged from 0.56${sim}$3.60 mg $L^{-1}$, 0.03${sim}$7.29 mg $L^{-1}$, and 0.002${sim}$0.754 mg $L^{-1}$. Chlorophyll- a was extensively changed from 2.29 ${mu}g;L^{-1}$ to 136.28 ${mu}g;L^{-1}$ by month and stations. Results of nutrients indicated the eutrophic level in this area and water quality was the gradual worsening in the lower stations than those of upper stations during the period studied. The Pearson correlation analysis between the concentration of chlorophyll- a and the environmental factors indicated that BOD, COD, pH, $NH_4;^+$-N, TP, TN, conductivity and $PO_4;^{3-}$-P were positive correlation, but $NO_3;^-$-N was negative. The environmental factors investigated using the principal component method could be triparted. The first factor group included conductivity, BOD, COD, TN, TP, $NH_4;^+$-N, $PO_4;^{3-}$-P and SS, the second WT and DO, and the third pH and $NO_3;^-$-N. Using the stepwise regression analysis, chlorophyll- a was under the influence of conductivity, $PO_4;^{3-}$-P, $>NO_3;^-$-N and $NH_4;^+$-N Chlorophyll-a = 0.3661 ${ imes}$ (Conductivity) - 0.3592 ${ imes}$ ($PO_4;^{3-}$-P) - 0.3449 ${ imes}$ ($NO_3;^-$-N)+0.4362 ${ imes}$ ($NH_4;^+$-N.