Agroindustrial by-products have become an economical and ecofriendly alternative for wastewater treatment because their lignocellulosic structures are prone to adsorb metals and dyes from solutions. Mauritia flexuosa petioles are discarded during fiber extraction from leaves and are becoming an abundant agrowaste product. This study characterizes the biomass from Mauritia flexuosa petioles using different spectroscopic techniques and evaluates aqueous Cu(II) and methylene blue adsorption on this biomass. The results showed that Mauritia flexuosa petioles are a mesoporous and lignocellulosic biomass, rich in carboxyl and hydroxyl groups that adsorb Cu(II) and methylene blue primarily through physical and exothermic processes. Copper and methylene blue had adsorption rates of 0.016 and that are mainly controlled by the ─ COOH and ─ OH groups presented in the biomass surface. Copper adsorption occurs through liquid film diffusion and electrostatic attraction, whereas methylene blue adsorption occurs through electrostatic attraction and hydrogen bonding. The maximum Cu(II) and methylene blue adsorption capacity was 14.20 and , respectively. These findings make this biomass a novel low-cost adsorbent and contributes to agrowaste valorization and reuse.