Heavy-metal pollution (such as Cd(II)) is regarded as a serious environmental problem, posing a great threat to human beings. In this research, a novel water-dispersible magnetic alginate/hydroxyapatite composite with high-efficiency Cd(II) adsorption performance was successfully synthesized by a facile wet-chemical method. The magnetic separation experiment and magnetic property analysis indicate that a magnetic alginate/hydroxyapatite composite can be effectively separated under a magnetic field. The zeta-potential result and dispersity experiment indicate that the lowest zeta-potential is –39.4 mV at pH = 5, and the obtained sample dispersed well in a Cd(II) solution after 120 min. The maximum adsorption capacity of a sample on Cd(II) is 135.3 mg g–1 at pH = 5, and the adsorption of Cd(II) reached equilibrium in 10 min. The adsorption data could be fitted well using the Langmuir model, and the adsorption kinetic follows a pseudo-second-order kinetic model.