A flexibilized resorcinolic novolak resin is prepared by reacting a phenolic compound, such as resorcinol, with an unsaturated dihydroxy, an unsaturated aldehyde, an aliphatic dialdehyde, or a mixture thereof. An aldehyde (different from the unsaturated aldehyde and the aliphatic dialdehyde) is either simultaneously or subsequently added to the reaction mixture. The flexibilized resorcinolic novolak resin can be used in an adhesive composition for enhancing the adhesion between tire cords and rubber for tire applications.