The inhibitory effects of Avena sativa L. seed extract were studied on life history of Sitotroga cerealella Olivier (Lepidoptera: Gelechiidae). Although, chronic ingestion of A. sativa inhibitor (I10) did not show significant reduction of the growth and development of S. cerealella; a delay in the developmental time of immature stages was detected when S. cerealella larvae were continuously fed on I30 and I50 concentrations of the inhibitor. The highest fecundity was recorded for females which came from larvae fed on I10 concentration (102.46±2.50 eggs/female), and the lowest fecundity was observed for females which came from larvae fed on I50 concentration (31.64±3.17 eggs/female). The lightest pupae of S. cerealella were observed on I50 concentration (2.76±0.07 mg). The lowest glycogen and lipid contents of the pupae were detected on I50 concentration (50.00±3.53 and 289.57±29.00 µg/pupa, respectively). The inhibitory studies indicated that A. sativa proteinaceous extract is a good candidate as an inhibitor of the α-amylase of this pest. This inhibitor can be expressed in genetically engineered plants to confer resistance to S. cerealella.