PURPOSE: To economically obtain a compd. useful as an insecticide from a raw material easy to obtain by reacting 1,3,4-oxadiazole and a tertiary alkyl cation precursor in the presence of a strong acid catalyst.

CONSTITUTION: 1,3,4-oxadiazole and a tertiary alkyl cation precursor (e.g.; t-butanol) are reacted in the presence of strong acid (e.g.; sulfuric acid) in a solvent such as acetic acid at -20-150°C to obtain an objective compd. 1,3,4- oxadiazol is 2,5-disubstituted-1,3,4-oxadiazole and a substituent may be substituted by one to three 6-10C aryl groups, 5- or 6-membered hetero rings, 1-10C alkyl groups or 1-10C alkoxy groups. This compd. shows insecticidal activity especially against Coleoptera and Lepidoptera.