PURPOSE: To obtain an epoxy resin compsn. suitable for producing a coating compsn. capable of forming a coating film having excellent adhesion to a substrate and corrosion resistance by incorporating a particular group into a side chain and/or a terminal of the skeleton of a resin.

CONSTITUTION: A CN group is incorporated into a side chain and/or a terminal of the skeleton of a resin with the CN group content being pref. 0.01 to 10meq./g on a solid basis of resin, and this resin is used to prepare an epoxy resin compsn. (e.g. a compsn. contg. an epoxy resin obtd. by reacting a nitrile compd. contg. an amino group, e.g. 2-aminopropionitrile, with an epoxy resin, e.g. diglycidyl ether of bisphenol A.