Abstract: The isothermal oxidation kinetics of Zr₅₈Cu₁₆Ni₁₃Al₁₀Nb₃ bulk metallic glass were studied in both the glassy state(lower than T_g= 657 K) and the supercooled liquid region(T_g= 657 K < T < Tx= 759 K) by means of the thermogravimetric method for different oxidation durations(1.5 h and 126 h) in dry air. Comparisions on the oxidation products and the substrate structures,oxidation processed for 126 h at two different annealing temperatures of 623 K and 673 K were made.Results show that t-ZrO₂ with the amorphous substrate was achieved after isothermal oxidation for 1.5 h in the temperature range of 573 K—673 K. The oxidation rate is linear with the oxidation time at 623 K in the glassy state. However,the oxidation rate curve at 673 K shows three stages over time,the fast growth region(0—1 h),the growth rate reduced region(1—6.5 h) and the steady region with slow speed(6.5—126 h). Crystallization has close relationship with the oxidation mechanism in the supercooled liquid region during long oxidation time.