This study was conducted to analyzed of the characteristics of water quality in the inlet of Saemangeum.. Specifically hourly monitoring(25hr) performed from Feburary 2003 to October 2005. Variation of salinity was no diffirence between at MKB and DJB on the large time of tidal effect on the side DJB was more higher(p<0.01) salinity than MKB by on the small time of tidal effect and rainfall, therefore we know that the tide flow into toward DJB than MKB. Total suspended solids(TSS) increase by turbulence as seawater input. A principal component analysis(PCA) showed that salinity and TSS factors was opposite to TN and TP factors. Therefore we expected that there is no correlation between high TSS and a nutrient increase and seawater circulation have an effect on water quality improvement by dissolved oxygen supply and nutrients dilution. Also, there is very big difference between minimum and maximum values during hourly monitoring(25hr) of TSS(100~800mg/L), COD(4.0~12.0mg/L), TN(3.0~9.0mg/L) and TP(0.2~1.0mg/L) which showed a sine curve 『The lowest-increase-peak-decrease-The lowest』types. The variation of water quality explained by hourly monitoring(25hr) suggests that water quality environments of Saemangeum area may have cycle typical of estuary river depending on tidal effects.