BHCs and DDTs in a 210Pb dated sedimentary core in Macao estuary were analysed with supercritical CO 2 extraction and GC-ECD. The concentrations of BHCs in the core sediment dated from 1962 ranged from trace level (<MDL) to 82.4 ng/g, and those of DDTs ranged from trace level (<MDL) to 79.0 ng/g. The highest concentrations of both DDTs and BHCs were found in sediment dated 1993, which correspond to a sharp decrease in cultivated land area and a greatly expanded capital construction investment scale in Zhuhai in 1992–1994. Vertical variations of (DDD + DDE)/DDT and DDE/DDD ratios indicated that DDTs deposited after 1985 were subjected to more on-land weathering process than those deposited before 1985. The authors suggested that the organochlorine pesticide residue in soils might have been mobilized by large-scale land transformation, which greatly contributed, after the production ban, to the DDTs in sediments in Macao estuary. Significant decreases in concentrations of BHCs and DDTs were observed in sediments deposited after 1993.