To obtain the subject composition capable of rapidly reducing the spray particle diameter after spraying and maintaining the diffusivity of a chemical by adding a propellant to an insecticidal stock solution of a specific composition effective against pyrethroid-resistant Blattella germanica, etc.

This composition is obtained by adding (B) a propellant to (A) an insecticidal stock solution containing (i) 5-methoxy-3-(2- methoxyphenyl)-1,3,4-oxadiazol-2(3H)-one as an active ingredient and a solvent of (ii) methyldiglycol and (iii) ethanol in combination. The weight ratio of the ingredients (i) to (iii) is preferably 1:(0.5-5):(5-30). Dimethyl ether is preferably contained in an amount of ≥50% in the ingredient B. When the combination of the ingredients (ii) and (iii) is used as the solvent of the ingredient (i), a sufficient amount of the active ingredient is dissolved even with a small amount of the solvent to rapidly reduce the spray particle diameter after spraying. The diffusivity of a chemical can be maintained to provide the practically complete insecticidal aerosol composition.