A new conceptual bonding technique, "hyper-interfacial bonding" has been proposed as the most effective bonding technique for ultra-fine grained steels. The hyper-interfacial bonding process was characterized by the instantaneously surface-melted pressure-bonding which involved a series of steps, namely, surface heating by high frequency induction, rapid removing of a heating coil and simultaneously pressing of specimens together by an oil pressure system. All sequences were typically completed within a second under vacuum/gas atmosphere. An ultra-fine grained high strength steels with the average grain size of 1.0-1.5?m were used for bonding. The surface of specimen could be rapidly heated up and melted within about 0.2s. No voids existed on the bond interface and the primary ferritic phase was formed at bond interface. A bainitic structure and MA-constituents were confirmed in HAZ, while the base metal indicated the fine ferrite-cementite/pearlite texture. The maximum hardness in HAZ was limited at HV320-400 and the softening in HAZ did not occur consequently. Prior austenitic grains were coarsened at the vicinity of the bond interface, however, the grain growth in bond layer could be depressed below about 11-16?m attributed to the dynamic recrystallization during pressure-bonding process. The mechanical properties of joints attained to approx. 80% of base metal properties. It could be resulted that the hyper-interfacial bonding technique was a feasible joining method for ultra fine-grained steels.