Analyses have been made to extract the objective interfacial fracture toughness from the peel strength of very thin metallic films. An elastoplastic bending model of the adherend film has been employed in the analyses applying the fracture mechanics concept of steady-state interfacial crack growth. The analytic result finally shown is a universal peel diagram where the objective interfacial fracture toughness is readily readable when the peel strength is known. Experimental results for Cu films on Si and polyimide substrate systems with a Cr interface are also presented.