The effects of pH, initial dye concentration and temperature on the decolorisation of CI Reactive Black 8 by zero-valent iron powder (Fe-0) with or without ultrasonic irradiation were investigated. It was verified that the presence of ultrasonic irradiation enhanced the decolorisation of CI Reactive Black 8. The decolorisation efficiency decreased with increasing pH, but increased with increasing iron addition and temperature in both systems. Initial dye concentration had little effect on the decolorisation efficiency in either system.