Abstract: This study systematically investigated the precipitation behavior of QN1804 austenitic stainless steels with different Nb contents(0.05wt% and 0.08wt%) during isothermal aging at 800-1150 ℃ for 40-14400 s. The types of precipitates formed during the aging process were identified, and the corresponding precipitation kinetics curves were plotted. The results show that both steels exhibit C-shaped precipitation kinetics curves. With the aging temperature increasing, the incubation period for precipitation first decreases and then increases. Moreover, the overall precipitation process of the 0.05wt% Nb steel is delayed compared with that of the 0.08wt% Nb steel. During isothermal aging, the precipitation temperature range of Nb(C, N) in both steels is 800 ℃-1150 ℃, while that of the Z phase is 800 ℃-900 ℃ for the 0.05wt% Nb steel and 800 ℃-1000 ℃ for the 0.08wt%Nb steel. Both steels exhibit a nose temperature of 1100 ℃ on the precipitation-time-temperature curve, corresponding to incubation periods of 80 s and 60 s, respectively.