Suppression of the furylfuramide-induced SOS response by 25 kinds monoterpenoids (hydrocarbons, alcohols, ketones, and aldehydes) with a p-menthane skeleton was studied. Suppression of the SOS-inducing activity by monoterpenoids was determined in the umu test using Salmonella typhimurium TA1535/pSK1002. The terpene alcohols, ketones, and aldehydes had potent suppressive effects, but the hydrocarbons did not. Especially, (+)-menthol, (+)-pulegone, piperitenone, and cuminaldehyde were shown to have the most potent suppressive effects, and the ID(50) (dose for 50% inhibition) was 0.52 micromol/mL.