Studies on the persistence and dissipation of deltamethrin (C22H19Br2NO3) in two types of soil, namely peat and silty clay were conducted under laboratory conditions. The analysis was done using a gas chromatography (GC) equipped with an electron capture detector (ECD). The dissipation rate of deltamethrin was faster in silty clay soil than in peat soil at 25°C. When the temperature was increased from 25 to 35°C, the half-life of deltamethrin decreased by 32.53% in peat soil and 22.9% in the silty clay soil in the presence of light. When the same experiment was conducted in the dark, the decrease in the half-life of deltamethrin was 27.9% in peat soil and 22.5% in silty clay soil. When the soil moisture content was increased from 40 to 60%, the half-life of deltamethrin decreased by 50.7 and 19.75% in peat soil and silty clay soil, respectively. A significant degradation rate of deltamethrin was observed in non-autoclaved soil compared with that in autoclaved soil where the half-life was reduced by 76.05% in peat soil and 59.21% in silty clay soil. The results showed that the degradation rate of deltamethrin in soil had a direct relationship with the microbial activity in the soil.