In this study, a life cycle assessment (LCA) technique based on ISO 14040 series was performed to evaluate biodiesel production from freshwater microalgae Scenedesmus armatus in terms of energy efficiency (Net Energy Ratio or NER) and environmental impact (Global Warming Potential or GWP). The system boundary covered the entire life cycle of microalgae-based biodiesel, which was divided into four distinct steps: cultivation, harvesting, oil extraction, and transesterification. Based on a functional unit of 1 MJ biodiesel, NER was found to be 0.34 and 0.19 for mass allocation and energy allocation, respectively. This energy deficit (NER<1) for both allocation methods was due to the high energy input required to culture microalgae. However, CO2 uptake in biomass agriculture leads to better performance in global warming potential (GWP) when compared to conventional diesel and biodiesel produced from rapeseed and soybean. This is a result of the cultivation process in which microalgae can fix up to 25 % of net greenhouse gas emissions (kg CO2 equivalent). Sensitivity analysis showed that increasing in biomass concentration can improve not only net energy ratio (NER) but also global warming potential (GWP).