A series of 4-phenyl-acyl-substituted 3-(2,5-dimethylphenyl)-4-hydroxy-1-azaspiro[4.5]dec-3-ene-2,8-dione derivatives were designed and synthesized, and their structures were characterized using (1)H NMR (or (13)C NMR), mass spectrometry, and elemental analysis. The bioactivities of the new compounds were evaluated. These compounds exhibited good inhibition activities against bean aphids (Aphis fabae) and carmine spider mite (Tetranychus cinnabarinus), and 4-phenyl acyl esters showed stronger bioactivity than 4-arylesterases and alkyl esters. The results showed that compound 8-I-e, which contains a para-methoxy group on the phenyl acyl, and compound 8-I-m, which contains a para-trifluoromethyl group on the phenyl acyl, displayed potent insecticidal activity against A. fabae and T. cinnabarinus respectively. The insecticidal activity showed a clear structure-activity relationship, confirming the importance of the flexible bridge. The DFT/B3LYP/6-31(d) level method was used to calculate molecular geometries and electronic descriptors. These factors included total energy, charge distribution, and the linear orbital level of the title compounds. Quantitative structure-activity relationship studies were performed on these compounds using quantum-chemical and physicochemical parameters as independent variables and insecticidal activity as a dependent variable. Insecticidal activity was most closely correlated (r > 0.8) with quantum chemical and physicochemical parameters.