Fish scale of the species Leporinus elongatus was tested as an adsorbent for anionic Remazol dyes. Characterization has suggested that hydroxyl, phosphate, amides I, II, and III, and carbonate groups are the potential sites of adsorption. From solution calorimetry, values of thermal effects, Q int, and amount of dye that interacts, n int, were determined. The adsorption order observed was Yellow-dye/scale > Red-dye/scale > Blue-dye/scale. The Q int and n int data were successfully adjusted to the Langmuir isotherm model. The dyes removals by fish scale are exothermic processes (from −83 to −199 kJ mol−1) with negative entropies and are thermodynamically spontaneous. The thermodynamic results suggest that the interactions at scale/anionic dye interfaces occur mainly by surface reactions. It was finding that fish scale is a new and suitable sorbent material for recovery and biosorption/adsorption of anionic dyes from aqueous solutions.