ABSTRACT: Macroalgae have significant advantages over land-living biomass resources and are promising pivotal feedstocks for the onset of the blue bioeconomy. Among these, Ulva lactuca has demonstrated a high potential due to its wide distribution and high productivity. In this work, a detailed chemical characterization of U. lactuca enabled the identification of polysaccharides as the main macromolecular component of the organic fraction. They present a high diversity of sugar constituents and hence can be a relevant source of added-value oligosaccharides for the food/feed industries. Four processes, with increasing operational temperatures, were compared for the selective production of oligosaccharides: Conventional Soxhlet Extraction, Accelerated Solvent Extraction, Hydrothermal treatment (HT) and Dilute Acid Hydrolysis (DAH). All processes presented high oligosaccharide/monosaccharide ratios, with HT and DAH exhibiting the highest oligosaccharides yields (10.6 and 16.6 g/100 g initial biomass, respectively). These oligosaccharides were obtained under milder, more economic conditions than the reported for lignocellulosic (land) plants and can represent an important added-value income of the algae biorefineries and thus contribute to their economic sustainability. info:eu-repo/semantics/publishedVersion