We systematically investigated the Gilbert damping (α) and interfacial perpendicular magnetic anisotropy (K i) in magnetic tunnel junctions with a MgO-barrier/FeB/MgO-cap layered structure using the spin-torque diode effect. By increasing the MgO cap thickness, α decreased, whereas K i increased monotonically. Values down to 0.0054 for α and up to 3.3 erg/cm 2 for K i were obtained for a MgO cap thickness of 0.6 nm. The small α and large K i suggest that MgO-capped FeB is a suitable free layer for spintronics devices such as spin-torque oscillators and spin-torque magnetic random access memories.