Storage stabilization of compounds with an oxetane ring or oxetane rings, which are useful as ring opening polymerizable monomers, is improved by addition of basic compounds thereto. The basic compound is preferably an alkali metal hydroxide or an amine. The compound with an oxetane compound preferably has a substituent at the 3- or 2-position thereof. Addition amount of the basic compound is preferably 0.1 to 1,000 ppm by weight, more preferably 1 to 1,000 ppm by weight per the compound with an oxetane.