The insecticidal activities of active component isolated from Ruta chalepensis L. (Rutales: Rutaceae) leaves and its derivatives were examined using fumigant and contact toxicity methods against rice weevil, Sitophilus oryaze L. (Coleoptera: Curculionidae) adults. Administering the chloroform fraction of the methanol extract resulted in 87.7% mortality at $1.02mg/cm^2$ against S. oryzae adults, using a fumigant method. The insecticidal constituent of R. chalepensis leaves was isolated by chromatographic techniques, and identified as quinoline-4-carbaldehyde ($C_{10}H_7NO$). Based on the $LD_{50}$ values, the most toxic compound against S. oryzae was quinoline ($0.063mg/cm^2$), followed by quinoline-4-carbaldehyde ($0.084mg/cm^2$), and quinoline-3-carbaldehyde ($0.173mg/cm^2$) using the fumigant method. In the contact method, the most active compound against S. oryzae was quinoline ($0.057mg/cm^2$), followed by quinoline-4-carbaldehyde ($0.065mg/cm^2$), and quinoline-3-carbaldehyde ($0.092mg/cm^2$). Changing the position of aldehyde groups in the quinoline skeleton increases the insecticidal activities against S. oryzae. Furthermore, these results suggest that naturally occurring quinoline-4-carbaldehyde and its derivatives could have potential for managing populations of insect pests affecting stored food products.