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 R_L indicated a favorable adsorption (0 < R _L < 1). Langmuir constant (K_L, i.e., 0.15) symbolizes that there is high affinity of the adsorbent for the adsorbate. The value of Freundlich constant was found to be 2.78 (n>1), 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 q_t agreed with the experimental value of q_t 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.