Polyacrylate (PAANa) and polyethylenimine (PEI) were used as complexing agents to combine with nickel ions. This complexation solution was transferred to the ultrafiltration cell and the separation by polyethersulfone (PES) ultrafiltration membranes was carried out under the pressure of 0.1 MPa. Effects of solution pH and polymer/Ni2+ mass ratio on nickel removal were investigated. The complex reaction equilibrium constants were calculated according to Langmuir isotherm model. Effects of concentration time on nickel removal and membrane flux were also studied. With PAANa as a polymer, the removal rate of nickel went the highest to 99.5% at pH 8 with PAANa/Ni2+ ratio of 5. When PEI was used, the removal rate of nickel ions went highest to 93.0% at pH 7 with PEI/Ni2+ ratio of 5. Best-fit complexation equilibrium constants at different pH values showed that pH 7 was most beneficial to the complex reaction. In addition, the number of nickel ions bound to a single monomer complexing agent increased with increase of pH value. During 12 h ultrafiltration process, the decline of membrane flux was less than 10% with PAANa as the complexing agent, while the membrane flux remains the same when PEI was used. The removal rates of Ni2+ kept constant with both complexing agents. Results showed that complexation-ultrafiltration can effectively remove nickel from aqueous solution at appropriate conditions.