The effects of environmental factors on bioactivity, adsorption and persistence of pretilachlor were studied in the laboratory and greenhouse using cucumber (Cucumis sativus L.) as the bioassay species. The three soils studied viz. Bernam, Selangor and Sabrang series were chosen for their different characteristics. The half-life of pretilachlor decreased from 10.24 to 4.90 days as temperature increased from 25°C to 35°C in the Selangor Series soil and from 10.86 to 7.63 days in the Bernam Series soil at 60% field capacity. At the same moisture level, an increase of temperature from 25°C to 35°C also reduced the half-life of pretilachlor in Sabrang soil from 8.87 to 2.59 days. The half-life of pretilachlor also decreased with increasing moisture levels in Selangor and Sabrang series but not in Bernam series soils. The greatest adsorption of pretilachlor was observed in Bernam series, followed by Selangor and Sabrang series. No phytotoxic residue of pretilachlor was detected in the supernatant after 10 h incubation. Since the residue was strongly adsorbed in Bernam series, its biological activity was less than in the other soils studied.