Methylene blue (MB) is a widely used industrial dye that poses significant environmental risks when discharged into aquatic systems. This study evaluated the performance of two unmodified agricultural byproducts (jackfruit seed powder (JSP) and tamarind tree bark powder (TTBP)) as low-cost and indigenous adsorbents for removing MB from synthetic aqueous solutions. The adsorbents were applied in their raw forms without chemical modification, and their physicochemical properties were characterized using scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, and X-ray diffraction (XRD) analyses. Batch adsorption experiments were conducted to investigate key operational parameters, adsorption behavior, equilibrium characteristics, and kinetics. Both adsorbents demonstrated rapid adsorption, with a substantial fraction of MB uptake occurring within the first 5 min and equilibrium reached within 30 min. JSP achieved a maximum removal efficiency of 85%, while TTBP showed a higher removal efficiency exceeding 93% under optimal conditions. The equilibrium data were well described by the Langmuir and Freundlich isotherm models, yielding maximum monolayer adsorption capacities of 108 mg/g for JSP and 125 mg/g for TTBP. Kinetic analysis indicated that the adsorption process followed the pseudo-second-order kinetic model. Overall, the results demonstrate that these readily available and chemically unprocessed biomaterials may serve as cost-effective alternatives to conventional adsorbents for dye removal.