Susceptibility of eggs, nymphs and adults of greenhouse whitefly (Trialeurodes vaporariorum Westwood) and adults of green peach aphid (Myzus persicae Sulzer) to pirimicarb (Pirimor®) and citowett oil alone vs. in combination was evaluated under greenhouse conditions. The glass vial and leaf dipping methods were employed for bioassay of adults vs. the immature stages (egg, nymph and pupa) of greenhouse whitefly respectively. Green peach aphid adults were treated through spraying technique. LC50 values of pirimicarb for greenhouse whitefly adult, egg and nymph stages were estimated 0.08, 2.55 and 0.98 g/l respectively, while the LC50 values of citowett oil for those developmental stages were estimated 2.58, 1.31 and 0.25 ml/l in the same previous order. The LC50 values of pirimicarb and citowett oil for adults in the case of green peach aphid were 0.04 g/l and 0.14 ml/l respectively. For a determination of the compounds interactions, the LC25 values of pirimicarb and citowett were assessed and a mixture of these compounds applied at a concentration of their LC25 rate. The mixture caused a mortality rate of 65.18, 65.55 and 66.85% on the adults, eggs and nymphs of greenhouse whitefly respectively and resulted in mortality of 68.92% on the adults of green peach aphid. Mortality resulted from the mixture was greater than that of pirimicarb at the concentration of LC50, hence, a noticeable synergistic effect observed. It was concluded that due to the cheap price of citowett oil, compatibility with environment and also synergistic effect on pirimicarb, a mixture application of these compounds at the concentration of 0.339 ml/l citowett oil and 0.372 g/l pirimicarb could be recommended for simultaneous control of greenhouse whitefly as well as green peach aphid.