Abstract: A method for bonding a restorative composite resin to dentin which comprises:treating the surface of dentin with a dentin-treating liquid for, 1 to 90 seconds obtained by adding glutaraldehyde and ferric chloride to an aqueous solution of ethylenediaminetetraacetic acid regulated to a hydrogen ion concentration (pH) of 7.4; removing the treating liquid by water-rinsing to dry the thus treated surface of dentin; applying a primer comprising an ethylene related unsaturated monomer, a (meth)acrylic ester polymer and tri-n-butyl borane on the dried surface of dentin; and filling the restorative composite resin onto the applied surface of dentin.