ABS, Alkyl benzene sulfonate, persists for long periods in stream because of its resistance to biologic degradation. Its bio-degradation is very varied in the environments. This investigation was therefore undertaken in order to know the biodegradation of synthetic detergents which are comprising soft and hard forms from February 1976 to September 1976. The biodegradations by spontaneuos settling and aeration were determined. The reduction rates of ABS, DBS, and LAS were 9.8%, 13.7% and 10.4% by the settlings for 5 days at $25^{circ}$ and 63.3%, 27.2%, and 43.9% by aeration respectively. It was not contributed effectively to biodegradate the synthetic detergents by the simulaneous incubation with micro-organisms isolated from sewage such as Enterobacter sp., E. coli, Bacillus sp., Flavobacterium sp., Pseudomonas sp., Staphylococcus sp., and etc. Tricking filter could also eliminate some amount of detergent. By the application of this investigation, it could be designed that detergents would be regulated in abuse in context with water pollution and be treated at a proper process in the sewage treatment plant to be installed.