The removing of toxic heavy metals from aqueous solution by agricultural biosorbents was investigated by studying the effect of nano sized (Delonix regia) and chemically modified biosorbent citric acid Delonix regia (CADR) for removing of Pb2+ ions. TEM, XRD and EDS, FT-IR, SEM methods were used for characterizing
the biosorbent(Delonix regia). The effect of contact time, pH,temperature, dosage of biosorbent, and Pb2+ ion concentration on adsorption process were studied. The maximum biosorption capacities (qm) of Pb2+ by Delonix regia biosorbent was 43.62 mg/g. The highest R. E was (93.5%) at pH 5. FT-IR method showed that the adsorption of metal ions occurs by functional groups on the surface of Delonix regia powder. The biosorption process was endothermic from thermodynamic parameters. The pseudo second-order model more fit (R2 =0.999) than the pseudo first-order model (R2 =0.985) from studying the kinetic parameters. The experimental data fit with Freundlich isotherm (R2 close to 1). Thisresultsindicated that Delonix regia is available agricultural, low cost and environment friendly biosorbent for removing the Pb2+ ions.