A soluble lignin derivative having an amino group was synthesized by a technique based on dry method by the reaction of isolated lignin from guava leaves with thiourea. The factors affecting the nitrogen content of the produced modified lignin mainly: reaction temperature, time and sodium hydroxide concentration besides the concentration of thiouria were studied and discussed briefly. It was concluded that higher nitrogen content of lignin derivative is obtained at reaction temperature 90^oC for reaction time 90 minute. Moreover increasing the amount of thiourea was accompanied by an increase in nitrogen content until a certain ratio. Product obtained was characterized by FT-IR, Thermo gravimetric analysis TGA, elemental analysis (C, H, N, and S). Nevertheless, the adsorption efficiency of metal ions as Zn, Cu, Ni, Cd, Co, V and Fe was determined using atomic absorption spectrometry (AAS). The flocculation performance of the obtained modified lignin was evaluated in terms of turbidity, organic matter, total hardness and total silica. It was observed that the best clarification doses were at 26 ppm ferric chloride and 4ppm modified lignin. This combined dose gives the lowest values of turbidity, total alkalinity, organic matter and total silica which changed from (18.2 NTU, 121ppm, 17.3ppm and 21.8ppm) to (0.97 NTU, 107ppm, 10.89ppm and 7.15ppm) respectively. It was found also that the modified lignin has high efficiency for removal of elements. For instance, as much as 75% of (Ni²⁺, Zn²⁺, Co²⁺, Cd²⁺, Mn²⁺) were removed by using (8 ppm) of modified lignin, and 95% removal of (Fe and Cu).