Profenofos (Selecron 72 % E.C.), and metalaxyl (Ridomil Gold Plus (42.5 % W.P.) were sprayed on field – grown onion plants at the recommended rates of 0.54 and 0.17 Kg. a.i./ Fed., respectively. Commercial products from (Ridomil Gold Plus) contained mixtures of metalaxyl as the active ingredient with low rates of residual protective fungicides, such as copper. Samples were collected at hour to 18 days after application and analyzed to determine the content and dissipation rate of aforementioned pesticides. Profenofos and metalaxyl residues were quantified by using gas chromatography, while copper by atomic absorption. The results showed that the amount of residues recorded during the experimental period, varied for each insecticide to another. The initial deposits of profenofos; metalaxyl, and copper on and in green onion were 3.50; 4.04, and 95.80 mg/kg, respectively. These amounts decreased gradually till reached 0.08; 0.53 and 1.18 mg/kg. after 14 days of spraying. The dissipation of profenofos was faster than metalaxyl, and copper. The corresponding half-life values were 0.91; 3.92, and 7.70 days, respectively. According to the maximum residues limits (MRLs) of profenofos (0.5 mg/kg.), metalaxyl (2.0 mg/kg.) and copper (30 mg/kg), were reached after 12, 12 and 5 days, respectively.