Abstract: Hydrogels were synthesized by the crosslinking between acetic acid lignin and isocyanate (NCO)terminated polyurethane ionomers (IPUI). The hydrogel prepared with the mass ratio of m(AAL)/m(IPUI)=0.35 presented maximum swelling ratio (3.14) in pH=6.8 buffer solutions. The results of thermo gravimetric analysis show that the thermal stability of the hydrogels is improved by the introduction of lignin. The hydrogels are used as coating material for ammonium sulfate and the data of release experiments for ammonium sulfate suggest that the hydrogels can be used as coating materials to prepare slow release fertilizer.