In many organisms, detoxification enzymes play important roles in detoxification of xenobiotics and are considered as biomarkers of toxic effects of exposure to a variety of these agents. In the current study, the effects of thiamethoxam and pirimicarb in sublethal concentrations were evaluated on Aphis fabae Scopoli (Hemiptera: Aphididae) detoxification enzymes. The median lethal concentrations for the female aphids exposed to thiamethoxam and pirimicarb were 113.85 (68.94-625.16) and 2.94 (1.71-3.99) mg (ai)/L, respectively. The activity of monooxygenases was measured as detoxification enzymes. The effects of both insecticides on A. fabae caused significant increase in monooxygenase (P<0.0001). Glutathione-s-transferase (GST) was likewise induced in A. fabae by increasing the sublethal concentrations of pirimicarb (df=5, 12, F= 18.17, P= 0.0001). Finally, thiamethoxam in higher concentrations (48.07, 75.06 and 113.85 mg (ai)/L) induced this enzyme (df=5, 12, F= 9.15, P= 0.0009). The results illustrate that two important aphicides, thiamethoxam and pirimicarb in sublethal concentrations can be detected by detoxification enzymes as biochemical markers. Consequently, prediction of poisonous effects on the aphid populations in the field will be possible