The present research deals with the synthesis and viability of Sawdust biochar/Fe3O4 nanocomposite toward textile waste water treatment. The structure, functionality, and morphology of the nanocomposite were determined by FT-IR, powder XRD, and SEM. Removal of the textile dye Reactive Blue 21 (RB21) was almost 75% under optimum conditions. The value of Langmuir dimensionless separation factor RL indicated a favorable adsorption (01), hence denoting favorable sorption. The negative values for free energy indicated a spontaneous reaction. Positive value for enthalpy suggested the endothermic nature of adsorption. The kinetic data showed a pseudo first-order kinetic model. The calculated value of qt agreed with the experimental value of qt at equilibrium. The results depicted that sawdust biochar/Fe3O4 nanocomposites are efficient adsorbents for removing RB21 and has potential application in treatment of textile wastewater.