We have successfully synthesized a high-recovery material for mercury based on a polyallylamine (PAA) hydrogel bearing thiourea cross-linking points and pendant amino groups. Adsorption of Hg-II was not significantly influenced by pH, and the PAA hydrogel was also able to adsorb Hg-II at a wide pH range (1-9) with high adsorption efficiency (>= 93%). Adsorption was fast in the first 10 min, with 84% adsorption efficiency, and equilibrium was reached within 30 min. Langmuir and Freundlich isotherm models were employed to correlate the experimental data. The adsorption of Hg-II by PAA hydrogel is well supported by a Langmuir isotherm model with a maximum adsorption capacity of 2.375 g(Hg)/g(gel), which is greater than those of other polymers in the literature. The PAA hydrogel was also to adsorb efficiently in a low concentration Hg-II aqueous solution (0.2 ppm). This polymer will be applicable as a high recovery material for mercury.