In this work, we discuss the ammonium nitrogen adsorption and reusability from aqueous solution by using poly(sodium acrylate) (PANa) hydrogels (Polymers 1–6) under different amount of crosslinker and initiator. The PANa hydrogels were synthesized from the neutralized acrylic acid (AA) monomer via free radical thermal polymerization by using ammonium persulfate (APS) as an initiator and N,N′‐methylene‐bisacrylamide (MBA) as a crosslinker. These polymers exhibited glass transition temperatures (Tg) of 68–88°C and Td values (5% weight loss temperature) in the range of 190–221°C under nitrogen atmosphere. The PANa hydrogels had swollen ratios ranging from 387 to 4,063%, related to the crosslinking density. The final equilibrium adsorption capacity of the polymers was in the range of 20–39 ppm with an initial ammonium nitrogen concentration of 100 ppm. Among them, Polymer 3 without MBA crosslinker displayed the highest swollen characteristic along with the most efficient adsorption capacity. In comparison, the as‐prepared high crosslinking density hydrogels showed relative lower adsorption capability but higher reusability. The polymer composition in this work determines the ability to absorb and desorb ammonium nitrogen compound.