Laminaria digitata (L. digitata) and Saccharina latissima (S. latissima) are the most common species of macroalgae in the north Atlantic and north Pacific. Because of their interesting composition, they have recently attracted attention as useful biomass for various purposes such as for biochemicals and bioenergy production. Nevertheless their composition varies according to the season and to the local environmental conditions. Therefore, in this study different samples harvested throughout a year and in different locations in Denmark were analyzed. The aim of the study was identifying the best period of the year and location to cultivate macroalgae for biofuels and biochemical production. Therefore, the biogas potential and the total phenolics profile for L. digitata and S. latissima were determined. The total phenolics were determined as they may represent an interesting bioactive compound, due to their significant health benefits. The highest methane yield (358.9 ± 5.1 and 285.0 ± 19.1 N mL of CH 4 g −1 of volatile solids for L. digitata and S. latissima, respectively) and total phenolic content (TPC) content (47.4 ± 0.0 mg of TPC g −1 of dry matter for L. digitata) were recorded in summer when the sugar level and the light intensity reached their maximum.