Recent advancement was the use of laser radiation to photobiostimulate the methanogenic bacteria in order to increase the biogas and methane production from the anaerobic digestion (AD) of livestock manure. However, the environmental impact of using the laser radiation as anaerobic bacteria stimulator still not evaluated. The objective of this paper is to conduct a comparative environmental impact evaluation of manure treatment with different laser radiation times for biogas production. A life-cycle assessment (LCA) methodology was implemented for this purpose. The treatments under evaluation were 0.5 h,1 h and 2 h of laser irradiation compared to 1 h incandescent lighting and the control (neither laser irradiation nor light was used). The highest biogas yield, methane content and overall Energy were achieved with 0.5 h laser irradiation and were 335251 m(3), 63.1% and 2043353 kWh, respectively. The results were presented in the form of the specific impacts on global warming and greenhouse gas (GHG) emissions mitigation of producing and utilizing biogas as an energy source. It was concluded that the photobiostimulation of anaerobic bacteria using laser irradiation has no negative environmental impact compared to the control, where no irradiation was applied. (C) 2019 Elsevier Ltd. All rights reserved.