To obtain an insecticidal composition capable of controlling a bad influence on human body, safely usable, effective against, insect pests against wood and tatami by making the composition include an antimicrobial and mildewproofing agent, a synthetic resin and a solvent.

This composition comprises (A) an antimicrobial and mildew proofing agent, (B) a synthetic resin and (C) a solvent. Preferably the composition substantially does not contain an insecticidal component for killing insect pests against wood and tatami. A solvent containing a lactic ester such as ethyl lactate, etc., is preferably used as the component C. For example, preferably the composition comprises 1-10 wt.% of the component A such as 2-(4- thiazolyl)benzimidazole, etc., 5-60 wt.% of the component B and ≥10 wt.% of the component C.