Abstract: In 10 L aerobic completely stirred tank reactor, the effect of hydraulic retention time (HRT) on the amount, molecular weight (Mr) distribution and components of soluble microbial products (SMP) in effluent was investigated under the three concentrations of influent COD of 1 000, 1 500 and 2 000 mg/L for the substrate of glucose. The amount of SMP manifested the trend of reduction with the prolongation of HRT at the same concentration of influent COD, and increased with the concentration of influent COD at the same HRT. With the longer HRT, the percentage of the low Mr fraction (Mr<1×103) of SMP increased initially and then decreased, that of the medium Mr fraction (1×1031×104) reduced gradually. The HRT had considerable effect on the content of polysaccharide and protein in SMP, and had no considerable effect on that of DNA. With the prolongation of HRT, polysaccharide and protein degraded gradually.