Incubation experiments were conducted to examine the effects of activated sludge on degradation of chlorate in soils. The results show that application of activated sludge could significantly promote the decomposition of soil chlorate though the degradation rate of chlorate did not necessarily increase with increasing application rate of the sludge. The effectiveness of activated sludge on soil chlorate degradation was significantly affected by temperature, moisture content and pH. There is a tendency that the rate of chlorate decomposition increased with increasing temperature and moisture content until optimal values of temperature and moisture content were reached. This can be attributed to the enhanced activity of chlorate-reducing microorganisms in hot and more reducing soil conditions. Soil pH also had important controls on the decomposition of chlorate. The experimental results demonstrate that neutral pH more favoured the degradation of soil chlorate, compared to either acidic or alkaline pH. While soil organic matter content could affect chlorate decomposition, its impact on the effectiveness of activated sludge on chlorate degradation was minor. This study has implications for developing cost-effective techniques for remediating chlorate-contaminated soils, particularly in the longan-producing countries. (C) 2008 Elsevier B.V. All rights reserved.