Abstract: In order to study microbial activity decay rates and physical property changes in activated sludge during a starvation period, as well as the recovery after restarting, this paper studied the impact of alternating aerobic (ρ(DO)=5.50 mg/L)/anoxic(ρ(DO)≤0.03 mg/L) starvation conditions on sludge activity in a two-stage sequencing batch reactor (SBR) under stable operation. Changes of the recovery ability and the physical and chemical properties of the sludge were also researched. It was shown in the results that after a starvation period of 30 d, the COD_Cr removal rate decreased by 20.8%, heterotrophic bacterial activity (r_COD) decreased from 111.8 mg/(L·h) to 59.2 mg/(L·h), and the NH₄⁺-N removal rate decreased by 59.2%. In addition, they were recovered at the 94^th day, 97^th day and 95^th day, respectively. The decay rate of ammonia oxidizing bacteria (AOB)(k_AOB) was 0.029 d^-1. The decay rate of nitrite oxidizing bacteria (NOB)(k_NOB) was 0.021 d^-1. In the earlier stage of recovery, the recovery rate of AOB (k_AOB′=0.125 d^-1) was higher than that of NOB (k_NOB′=0.069 d^-1), which led to accumulation of NO₂^--N. In addition, due to the starvation period, the sludge concentration (MLSS) decreased by 42.6%, the sludge index (SVI) increased from 71.2 mL/g to 135.1 mL/g, and the concentration of extracellular polymeric substances (w(EPS) expressed by VSS) decreased from 37.9 mg/g to 18.5 mg/g, which mainly referred to the decrease in protein content. Changes of the physical parameters could be recovered in the recovery period.