The objective of this research was to study the efficiency of water hyacinth (Eichhornia crassipes) for removing chlorpyrifos in water. At initial chlorpyrifos concentrations of 0, 0.1, 0.5 and 1.0 mg/L, the relative growth rates (RGR) of E. crassipes were significantly increased, giving an observed dry weight based RGRDW for E. crassipes of 0.041, 0.039, 0.038 and 0.036 mg/g/day. The disappearance rate constants of chlorpyrifos in the control (no plants) at chlorpyrifos concentrations of 0.1, 0.5 and 1.0 mg/L were 3.52, 2.29 and 1.84 µg h-1 and in water hyacinth at chlorpyrifos concentrations of 0.1, 0.5 and 1.0 mg/L were 17.19, 10.16 and 7.16 µg h-1, respectively. The accumulation of chlorpyrifos occurred in this descending order: roots >stems >leaves. The maximum concentration of chlorpyrifos in roots, stems and leaves were 290.1, 125.4 and 98.9 mg/kg dry weight, respectively, at the day 3, 6 and 8. The accumulation of 3,5,6 trichloro-2-pyridinol occurred in this descending order: leaves >stems >roots. The maximum concentration of 3,5,6 trichloro-2-pyridinol in leaves, stems and roots were 13.8, 11.8 and 9.7 mg/kg dry weight, respectively, at the day 10, 7 and 5.