The leaching of heavy metals may be done by the ratio of the quantity of a heavy metal extracted out through toxicity characteristics leaching procedure (TCLP) to its total concentration. This experiment is usually applied to evaluate the leachability of heavy metals in the compost, soil, or sediment. The fact that the leachability of Cu and Zn was reduced might be due to formation of Cu complex with organic matter or humic-like substances at the end of the composting process. Leachability of Ni, Pb, and Cd contents were not detected during the agitated pile composting process of water hyacinth. The leachability of Zn, Mn, Fe, and Ni increased approximately 5%, whereas the leachability of Cd and Cr decreased up to 10% in zeolite in the composting process. Leachability of heavy metals decreased up to 15% in zeolite treatment as compared with control and 5% and 10% in zeolite treatments during the rotary drum composting of water hyacinth.