Unsustainable consumption and production patterns, together with industrialization and population growth, have increased the generation of municipal solid waste (MSW), causing several environmental problems. The European Waste Framework Directive (WFD) sets waste prevention, preparation for reuse and recycling as priority strategies. Nevertheless, still a great amount of MSW ends up in landfills and waste-to-energy (WtE) plants. WtE plants reduces waste volume and allows efficient recovery of energy, however, incineration results in various types of solid wastes, bottom, boiler and fly ashes (FA). Due to the concentration of dangerous substances, FA are treated by means of stabilisation/solidification (S/S), thermal treatments or combined treatments, to reduce their toxicity and to avoid negative impacts on the environment and human health. Among S/S alternatives, stabilisation with cement and carbonation are one of the most popular. To determine the environmental performance of these processes this paper conducted a life cycle assessment (LCA). The study evaluated FA stabilisation with cement and water and FA carbonation for 55 % and 100 % excess of CO2 in the flue gas at the outlet of the reactor, and pressures of 1, 5, 10, 15 and 20 bar. The results showed that the range of pressure between 3 and 4 bar, and 55 % excess of CO2 in the flue gas have an efficient performance. The comparison of FA carbonation and stabilization displayed that the latter has higher impacts than the alternative carbonation due mainly to the cement production and the reduction of lixiviation and CO2 capture in the ash.