To obtain an insecticidal composition or insecticidal aerosol agent having high immediate effect on insect pests.

This insecticidal composition comprises (a) 2-methyl-4-oxo-3-(2- propynyl)cyclopent-2-enyl 3-(2,2-dichlorovinyl)-2,2-dimethylcyclopropanecarboxylate and (b) at least one kind of ether compound selected from the group consisting of diethylene glycol monoalkyl ethers, diethylene glycol dialkyl ethers, triethylene glycol monoalkyl ethers and triethylene glycol dialkyl ethers. The insecticidal aerosol agent is characteristic in containing the above composition and a propellant.