This research was conducted to analyze the influence of the environmental factors on water quality such as pH, dissolved oxygen, and electrical conductivity of rainfall, throughfall, soil water(A and B layer), and stream water quality at a small forested watershed. Rainfall, throughfall, soil water(A and B layer), and stream water were sampled at the study sites in Kwanak Arboretum, Seoul National University in Mt. Kwanak for 14 months(Jul. 1, 1996∼Aug. 31, 1997). Average rainfall pH value was 6.06(ranged from 5.02 to 6.60). Acid rain frequency(less than pH 5.6) was 16.7% . The lowest rainfall pH value was 5.02. Average of pH values in hydrological processes were decreasing in the following order, stream water $gt; soil water [Prunus serrulata var, spontanea (B layer$gt;A layer)] $gt;throughfall(Prunus serrulata var. spontanea)$gt;soil water [Carpinus laxiflora(B layer $gt; A layer)]$gt; throughfall(Carpinus laxiflora) $gt; rainfall $gt; soil water [Pinus rigida(B layer $gt; A layer)] $gt;throughfall(Pinus rigida). pH values of throughfall in Prunes serrulata var. spontanea and Carpinus laxaflora were higher in Pines rigida. Average of dissolved oxygen values in hydrological processes were decreasing in the order, stream water $gt;throughfall(Carpinus laxiflora$gt; Prunus serrulata var, spontanea$gt; Pines rigida) $gt; rainfall $gt; soil water [Prunes serrulata var. spontanea(A layer) $gt; Pines rigida(A layer) $gt; Carpinus laxiflora(A layer) $gt; Prunes serrulata var. spontanea(B layer) $gt; Pines rigida(B layer)$gt; Carpinus laxiflora(B layer)]. And average electrical conductivity values in hydrological processes were decreasing in the order, soil water (B layer $gt; A layer) $gt; throughfall(Pinus rigida $gt; Prunes serrulata var, spontanea $gt; Carpinus laxiflora) $gt; stream water $gt; rainfall. Multiple regression equations of electrical conductivity and Mg^(2+), Na^+, total amount of cation, total amount of ion, and no. of before non-rain days in rainfall, throughfall, soil and stream water shows high significance(Multi R; 0.84).