This study successfully developed a low-cost adsorbent from compositing between magnetic nanoparticle (CoFe2O4) and dragon fruit peel-derived biopolymer (DFP-BP) and applied it to remove arsenite (As (III)) from contaminated water. The batch experiments were designed to study the influence of operational parameters on As(III) adsorption by nanocomposite (CoFe2O4@DFP-BP). With mapping analysis, the synthesized CoFe2O4@DFP-BP was characterized using SBET, SEM, FTIR, XRD, and EDS mapping. The As(III) adsorption mechanism was discussed based on material property data and isotherm and kinetic analysis. The result suggests that 5% is the best modification ratio on the CoFe2O4@DFP-BP for As(III) adsorption. The highest adsorption capacity of As(III) under the optimal conditions of pH 7, adsorbent dosage of 1.6 g/L, initial As(III) concentration of 2000 µg/L and the best described by the Sips model was 1922.7 µg/g. The adsorption kinetic followed pseudo-second-order, proving As(III) adsorption process controlled by chemisorption. The primary reaction pathway of As(III) adsorption on the CoFe2O4@DFP-BP5 was inner-sphere complexation through exchange between the nanoadsorbent’s surface and As(III) ions via oxygen-containing functional (carboxyl and hydroxyl) groups. The CoFe2O4 magnetic nanoparticles coated by biopolymer overcame drawbacks, including low stability and mechanical strength of biopolymer and agglomerate trend of magnetic nanoparticles. The adsorption process was highly reversible and accessible in the separation of nanoadsorbent after adsorption by the magnet. Therefore, the nanocomposite formed from solid waste has excellent potential as a material for removing As, contributing to sustainable development and feasibility in practical application.