With plasma oxidization to create an insulating layer of Al2O3, we have repeatedly fabricated some Ni80Fe20/Al2O3/Co magnetic tunnel junctions (MTJ), which show obvious tunneling magnetoresistance (TMR) effect. The insulating layer is well formed by the oxidization procedure, which is verified by optical spectra and other measurement results. At room temperature, the maximum TMR ratio reaches 6.0%. The switch field can be less than 800A/m and the relative step width is about 2400A/m. The junction resistance Rj changes from hundreds of ohms to hundreds of kilohms and TMR ratio decreases monotonously with the increase of applied junction voltage bias (under zero magnetic field).