The effects of LAS on Colifrom Bacteria which were prepared from the synthetic wastewater of BOD 1 and 9 milligrams per liter at concentrations of LAS l, 2, 4 and 6 milligrams per liter in 6 days at room temperature were studied- Total Coliform Bacteria was analyzed by Multiple Tube Fermentation Method. Biodegradation of LAS was detected by Methylene Blue Method. The results indicated that, in every concentration of LAS in the synthetic wastewater of BOD 1 and 9 milligrams per liter had the total Coliform Bacteria more than 2.4x1O(4) MPN/lOO ml. Therefore the effects of LAS on Coliform Bacteria was not evidence. It is because the big amount of pure culture of Coliform Bacteria was innocculated into synthetic wastewater, approximately 1.0X10(9) MPN/100 ml. It was also found that the biodegradation of LAS in the synthetic wastewater of BOD 1 milligram per liter was faster than in the synthetic wastewater of BOD 9 milligram per liter.