Macroalgae, so-called seaweeds, represent an innovative and sustainable substrate for biogas fuels production (third generation’s biofuels). However, large scale implementation are not yet commercialized due to high biomass production costs and in addition, low biomethane yields observed within some algae species preventing high energy conversion efficiency. The aim with this study was to investigate the impact of the enzymatic hydrolysis pre-treatment on the AD of macroalgae. Five brown macroalgae, A. nodosum and F. vesiculosus grown nearshore and A. esculenta, L. digitata and S. latissima grow offshore, were pre-treated with four different enzymes at 37 oC for 24 h. The biomethane yield was determined by anaerobic batch digestion test. The enzymatic pre-treatment improved the hydrolysis, where the biomethane yield of near- and offshore macroalgae was enhanced between 70 to 82 % and 12 to 48 %, respectively, compared with un-treated biomass. In addition the work present an economic analysis on the pre-treatment applied to a hypothetical full scale AD for biogas fuel production testing L. digitata and A. nodosum. Two cases presented, case 0 is based from the cultivation, harvesting and enzyme cost from literature and in case 1 the cultivation and enzyme cost reduced by 75 and 90 %, respectively. Reducing the cultivation and enzyme cost by 75 and 90 %, respectively, had a positive influence on the economy of the hypothetical large scale biogas plant.