The stochastic analysis was carried out to the hourly time series observed at Dae-gu, Wha-Myung and Ku-Mee in order to see water quality variation of the Nack-Dong River during Three months (July, Aug. and Sept.) in each year of 1979 and 1981. As a result of this study, it was found that 1. The simple correlation coefficients between some of the variables were fairly high. For example, the coefficients between Do and WT. were -0.824 (Dae-gu), -0.547 (Wha-myung), and -0.911(Ku-mee). The coefficients between COND and DO. were -0.263(Dae-gu), -0.347(Wha-myung) and -0.881 (Ku-mee). The coefficients between COND and WT. were 0.531 (Dae-gu), 0.361 (Wha-myung) and 0.800 (Ku-mee). 2. Hourly water quality time series of WT and DO existed as dominant 24 hours Periodicity For example, the Aut correlation coefficients about WT were 0.960 (K=1), 0.846(K=24), 0.691(K=48), 0.596(K=72), and 0.453(K=96). The auto-correlation coefficients of Do were 0.968 (K=1), 0.591 (K=24), 0.393 (K=48), 0.349 (K=72) and 0.250 (K=96). 3. Weekly water quality time series of WT and Do varied with the dominant 24 hours periodicity.