Oyster shell powder is a potential adsorbent material that can be used to control pollution in groundwater. The current research objective is to evaluate the heavy metal ion adsorption properties by oyster shell powder in an aqueous solution. Three kinds of heavy metals (copper, cadmium, and lead) were adsorbed using oyster shell powder from aqueous solution. The effects of different temperatures, contact times, pH values, and initial concentrations were examined in order to optimize the conditions used for heavy metal decontamination. Cadmium and copper adsorption behaviours were suitable for modelling by the Langmuir isotherm, and lead adsorption behaviour was best modelled by the Freundlich isotherm. Adsorption situations fitted a pseudo second-order kinetic model. Intraparticular diffusion of heavy metal ions by oyster shell powder could be divided into two stages: rapid diffusion first, followed by a stable second stage. The maximum adsorption amount was ranked in an ascending order as that to copper, cadmium, and then lead for both single and competitive systems. The adsorption capacities of copper, cadmium, and lead ions by oyster shell powder were lower in a competitive system than in a single system, indicating that competitive adsorption could occur.