The field experiment was carried out at Syngenta research station Kaha, city, El-kalubia Governorate, Egypt. Potatoes were transplanted in three field plots, each with an area 100 m2. A complete randomized block design (CRD) was applied with three replicates. A commercial formulation of Thiamethoxam (Actara 25% WG) was prepared and sprayed at the recommended dose (20 g 100 L1 water) using knapsack sprayer motor at mature plants were cultivated in plots consisting of eight rows. Common agricultural and fertilization practices were used. No insecticide sprays were applied to the test plots prior to or during this experiment. Representative samples about 1 kg were collected from various places of the experimental plots according to the FAO/WHO recommendations (FAO/WHO., 2006) approximately 2 h, 1, 3, 5 and 7 days after application of thiamethoxam. The samples were transferred immediately to the laboratory in an ice box. The samples were comminuted using the laboratory blender and stored at 4 C until analysis.