PURPOSE: The titled composition, prepared by adding a phenolate anionic product compound present in the form of a highly dissociated state at a high dissociation constant as a photopolymerization initiator to a photopolymerizable substance, and using a relatively inexpensive photopolymerization catalyst initiator, and having improved storage stability.

CONSTITUTION: A composition prepared by adding 0.1W20pts.wt. initiator obtained by reacting one equivalent phenolic OH in a phenolic compound, e.g. a monohydric phenol (derivative) such as (p-nitro)phenol, a dihydric phenol such as hydroquinone or bisphenol A or a polyhdric phenol such as pyrogallol or phloroglucin, with 0.001W1 equivalent compound useful for forming a salt, e.g. NaOH or Ca(OH)2, in a solvent inert to the salt formation, e.g. water or methanol, to 100pts.wt. photopolymerizable substance, e.g. a composition of an epoxy resin, acrylic acid and trimethylolpropane acrylate.