In this study, the organic matter of effluents from sewage treatment plants, located in the Nakdong watershed was investigated. Regression equations were computed using treated sewage data to convert the chemical oxygen demand(COD) concentrations, which are mostly available from an open database, into total organic carbon(TOC) concentrations. The average concentration of organic matter in the sewage treatment plant effluents were 2.2 16.8 mg/L for COD and 3.4 14.3 mg/L for TOC. The concentrations of COD were positively correlated with the TOC concentrations. The correlation between COD and TOC was relatively high, at 0.865(p<0.01). Based on these results, regression analysis was conducted. The regression equation for TOC was 1.651×CODMn-0.084 (R2=0.84). Furthermore, organic matter-related databases for more sewage treatment plants need to be built in order to establish TOC standards and manage the water quality.