Banana peel was used as the feedstock for the preparation of a magnetic adsorbent for the adsorption of methylene blue (MB) in aqueous solutions. The Fe-modified banana peel was characterized by surface and spectrometric methods. The Box-Behnken design (BBD) was used for determining the conditions of each experimental run and optimization of adsorption was achieved through response surface methodology. The R2, adjusted R2, and predicted R2 coefficients of the employed BBD model were determined as 0.9820, 0.9686, and 0.9182, respectively, indicating a high level of agreement between the experimental data and the proposed theoretical model. The optimum MB adsorption of 91.89% was achieved at an adsorption time of 50 min, temperature of 45 °C, adsorbent dosage of 2.5 g and MB concentration of 5 mg L−1. Equilibrium was achieved in 48 min. The most influential process parameter was the adsorbent dosage, whereas the impact of time, MB concentration and temperature was considerably smaller. The Langmuir Qmax value of 28.1 mg g−1 compared favorably to respective values from other published adsorbents.