Management of leachates generated by solid waste disposal is a very challenging aspect of landfill management in most parts of the world. In most developing countries, the leachates generated are discharged into the environment without treatment, leading to contamination of ground and surface waters and causing human health problems. Even though its potential risk has been established through chemical analyses, less work has been conducted on its effect on ecosystems. This study assessed the toxicity of leachates from three landfill sites of different ages from Ghana, namely Tema, Mallam and Oblogo, to aquatic organisms. Duckweed (Lemna minor) and crustaceans (Daphnia magna) toxicity tests were performed using exposures to concentrations of 6.25, 12.5, 25, 50 and 100 mL/L of the landfill leachates in control growth media. Physico-chemical properties of the leachates were also determined. The leachates from all the sites were toxic with IC 50 values ranging from 2.8 to 29.5%. The Oblogo landfill leachate (the oldest site) being most toxic to duckweed and Tema landfill leachate (the youngest site) most toxic to D. magna. Leachates characterized had varying concentrations of heavy metals (0.2-42.3 mg/L) with Cu and Cd below detectable limit. The organic component COD was below the permissible level (110-541 mg/L) and the TOC exceeded the permissible level (350-6920 mg/L). These results indicate that the age and other characteristics of the landfill sites contribute to the difference in the toxicity of the Ghana landfill leachates.