This study was performed to investigate the contamination degree of effluent from the sewage purification system and septic tank. The 711 samples, were collected from the large size tank located in Seoul from Mar. to June 1991. The results were as follows 1. The pH values of effluent were largely neutral of 6.96 in sewage and 7.43 in septic tank. 2. The average concentration of BOD was 48.18 mg/l in sewage and 127.0 rng/l in septic tank. 3. The average concentration of SS was 40.8mg/l in sewage and 90.5rng/l in septic tank. 4. In the analysis of nutrient salts, the average concentration of NH$_{3}$-N was 31.62mg/l in sewage and 88.79 mg/l in septic tank. 5. In the analysis of correlation among items, BOD, SS, NH$_{3}$-N and PO$_{4}$-P were higly correlated beween items. 6. As a results of above analysis, it is considered as desirable evaluation method of effluent not through the only item but through the integrated items.