Macroalgae is a key biomass for the development of circular economy. This study analyzes the environmental sustainability of a macroalgae production and conversion system in Denmark. A brown algae model based on Laminaria digitata and Saccharina latissima is utilized as feedstock for a biorefinery system which produces bioethanol, fish feed and liquid fertilizers. A Life Cycle Assessment was conducted from cradle to grave; i.e. from cultivation and harvest of biomass, to the use phase of the products.