A field study on the leaching and persistence of herbicide diuron in an oil palm agro ecosystem was conducted in an oil palm plantation in Sepang, Selangor. Two treatments, namely the recommended and double the recommended dosage of diuron were applied in the field trial. Diuron was sprayed using a knapsack sprayer (18 litres) at the rate of 0.3 kg ha^-1 (recommended dosage) and 0.6 kg ha-1 (double the recommended dosage). Soil samples were collected at different depths, viz. 0-10 cm, 10-20 cm, 20-30 cm, 30-40 cm and 40-50 cm at the following intervals: -1 day (before treatment), 0 day (day of treatment, 6 hr later), 1 day, 3, 5, 7, 14, 21, 30, 60, 90 and 120 days after treatment. Diuron residue was detected in the soil sampled at all depths, for both the dosages applied from day 0 to 60 days after treatment (DAT), with the exception of day 90 where it was only detected at the 0-10 cm depth when the plot was sprayed at double the recommended dosage. The calculated half-life of diuron when applied at both dosages was also determined and results showed that the half-life of diuron in soil when applied at the recommended and double the recommended dosage was in the range of 22.35 – 49.5 days and 18.73 – 57.75 days, respectively.