The açaí berry’s seed corresponds to 85–95% of the fruit’s weight and represents ~1.1 million tons of residue yearly accumulated in the Amazon region. This study confirmed that mannan is the major component of mature seeds, corresponding to 80% of the seed’s total carbohydrates and about 50% of its dry weight. To convert this high mannan content into mannose, a sequential process of diluted acid and enzymatic hydrolysis was evaluated. Diluted-H2SO4 hydrolysis (3%-acid, 60-min, 121°C) resulted in a 30% mannan hydrolysis yield and 41.7 g/L of mannose. Because ~70% mannan remained in the seed, a mannanase-catalyzed hydrolysis was sequentially performed with 2–20% seed concentration, reaching 146.3 g/L of mannose and a 96.8% yield with 20% solids. As far as we know, this is the highest reported concentration of mannose produced from a residue. Thus, this work provides fundamental data for achieving high concentrations and yields of mannose from açaí seeds.HighlightsMannan was confirmed as the major component (~50%) of açaí seeds.Diluted-H2SO4 hydrolysis had a limited effect on mannan conversion into mannose.Enzymatic hydrolysis was sequentially performed with a high seed concentration.Mannan was efficiently hydrolyzed by mannanases, producing a 96.8% yield.Mannose production of 146.3 g/L was obtained with mannanase-catalyzed hydrolysis.Graphical abstract