The adsorption and desorption behaviors of Hg²⁺ by living and dead Microcystis aeruginosa in aqueous solution were investigated. The results showed that both living and dead Microcystis aeruginosa can effectively adsorb Hg²⁺, the equilibrium adsorption capacity and rate increased with the increasing abundance of algae. The maximum adsorption amount of Hg²⁺ to living and dead Microcystis aeruginosa was 2.13×10^-2 and 1.11×10^-2 ng 10^-6 cells, respectively. The adsorption processes of Hg²⁺ by living Microcystis aeruginosa were biosorption and bioconcentration, whereas by dead Microcystis aeruginosa were only biosorption. Both pseudo-first-order and pseudo-second-order kinetics model can well describe the adsorption of Hg²⁺ by living and dead Microcystis aeruginosa, suggesting that adsorption processes might be predominantly controlled by a combined reaction of diffusion and chemical process. The adsorption characteristics were well illustrated by both Langmuir and Freundlich isotherm model, and Langmuir model can describe adsorption characteristics better. These demonstrated that there were strong interactions between Microcystis aeruginosa and mercuric ion, and Microcystis aeruginosa adsorbed Hg²⁺ were favorable processes through monolayer adsorption predominantly. The desorption processes of Hg²⁺ by Microcystis aeruginosa can be divided into three stages, i.e. the desorption amount of Hg²⁺ increased quickly within 0-60 min, the rate of desorption became very slow within 60-120 min, and tended to be balanced after 120 min.