The isothermal oxidation behavior of Zr58Nb3Cu16Ni13Al10 bulk metallic glass (BMG) under dry air in the glassy state and the supercooled liquid state (SLS) was studied by the thermogravimetric method. The oxidation rate and thickness growth speed in the SLS were both hugely higher than in the glassy state. The oxidation kinetics of BMG in both states for 1.5 hours was different, the parabolic law was followed in the glassy state at 300°C and 350°C, contrarily the linear law was followed in SLS at 400 °C. After the oxidation for 126 hours in SLS, the oxidation kinetics possessed two stages, the linear stage and the parabolic stage. The diffusion of the Cu2+ ion and CuZr intermetallic alloys were detected by GIXRD.