During the last decades, European institution establishes regulations which aim at protecting the environment from the adverse effects of the collection, treatment and discharge of waste water imposing wastewater treatment plants (WWTP) to release a good water quality in the environment. The constant diminution of the organic pollution of wastewater due to higher performance of water treatment through biological treatments leads to an increase in sludge production. The treatment processes used to concentrate and stabilize the sludge are of great importance as the sewage sludge treatment line can constitute 25 % to 72 % of total emissions of the WWTP [1]. Our study aims to present the sensitivity of Life Cycle Assessment environmental impacts results of a sewage sludge treatment line combining primary and secondary sludge thickening, anaerobic digestion, press filter dewatering, sludge storage and land spreading as final disposal (reference scenario) according to several types of parameters. Life Cycle Assessment of the reference scenario was conducting using GaBi software and environmental impacts results with the Recipe method. A sensitivity analysis was then conducted by changing reference value with a range of value for four types of parameters relevant of the treatment process performances. The studied parameters are: (a) Primary and secondary sludge composition (N, Volatile matter, P, K, Mg, Ca), (b) Anaerobic digestion performances (Volatile matter abatement, N mineralization rate, P solubilization rate, biogas composition, Hydraulic Retention Time) (c) Dewatering performances (dewatered sludge dry content based on literature value, dewatered sludge dry content based on pressure, cake thickness, filtration duration, N, P and K capture rate, polymer and FeCl3 dosage) (d) Primary and secondary thickening performances (thickened sludge dry content, N, P and K capture rate) By analyzing the sensitivity of each environmental impact (global warming, acidification, eutrophication, human toxicity…) according to each studied parameter, we identified several hotspots that research should be focused on to improve the efficiency of treatment performances and so the environmental impact of the whole sewage sludge treatment line.