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The Impact Assessment (IA) step in Life Cycle Assessment (LCA) studies is classified into three steps of characterization, normalization and weighting. In this research, various impact categories were weighted using Analytic Hierarchy Process (AHP), as a multi criteria decision making tool. Iranian tobacco production system was the example of agricultural system. The data for LCA analysis were collected from 225 farms. The data for AHP analysis were gathered by surveying 12 LCA experts. The results indicated that on-farm emissions of CO2, CH4, N2O, NH3, NOx and SO2 were accounted for 25, 96, 93, 99, 21 and 2% of the total emissions (cradle to farmgate), respectively. The characterization indices for the impact categories of acidification, terrestrial eutrophication, global warming, phosphate resources depletion, potash resources depletion and fossil resources depletion for one ton tobacco production were calculated to be 13.87 kgSO(2)eq, 19.69 kgNO(x)eq, 1883.90 kgCO(2)eq, 19.69 kgNO(x)eq, 4.19 kgP(2)O(5), 6.14 kgK(2)O, and 59,659.23 MJ, respectively. The LCA + AHP showed that the weighted factors of global warming, terrestrial eutrophication, acidification, fossil resources depletion, phosphate resources depletion and potash resources depletion were 1, 0.790, 0.518, 0.681, 0.422, and 0.263, respectively. Many agricultural systems could benefit from using the developed weighting factors for LCA studies in the agricultural sector. Based on the new developed weighted factors, the weighted indices of aforementioned impact categories for Iranian tobacco production were 0.24, 0.41, 0.19, 1.04, 0.23, and 0.20, respectively. This implies that fossil resources depletion impact category was attributed the highest negative environmental impacts of tobacco production followed by terrestrial eutrophication. (c) 2019 Elsevier B.V. All rights reserved.