PURPOSE: To provide the title promotor capable of providing an acid anhydride- epoxy resin compsn. having an excellent shelf stability at ordinary temp., a rapid curability at high temp., and various excellent characteristics, by reacting a reaction product of a metal alkoxide and boric acid with a specific amine.

CONSTITUTION: A reaction product prepd. by reacting a metal alkoxide (e.g., aluminum triisopropoxide) with boric acid is further reacted with a tertiary alkanolamine (e.g., triethanolamine) to prepare a solid reaction product, which is then finely pulverized to form a curing promotor for epoxy resins. The curing promotor is used in an epoxy resin compsn. comprising a carboxylic acid anhydride as the curing agent to provide therefor not only an excellent shelf stability and a rapid curability by heating but also a capability of being cured into a cured resin product having excellent electrical, mechanical, chemical and thermal characteristics.