Scale-up microcosm system consisting of producer, decomposer and predator was employed to assess effect of LAS on aquatic ecosystem. Effect of LAS was determined with not only population density but also chemical data such as ATP, nutrients, pH and DO, etc. Microorganisms such as bacteria, algae, protozoa and micrometazoa in the microcosm system proliferated and reached to stationary phase on day 16. In the stationary phase, values of biological and chemical factors were constant, supporting the dynamic equilibrium of scale-up microcosm. No observed effect concentration (NOEC) of LAS on population density was less than 1.5 mg·l−1. NOECs of LAS on ATP, DO and P/R (net photosynthesis/respiration) ratio were less than 2.5 mg·l−1. It was suggested that scale-up microcosm system was useful for environmental assessment because it could provide precise assessment of chemical substances based on biological and chemical condition of ecosystem.