Studies on the compositional proportion of characteristic microaggregates of 15 pairs of fertile and infertile typical brown earth and brown earth type paddy soil were carried out. Results showed that the proportion of(<10μm)/(>10μm) microa-ggregates could be used as an integrative index for evaluation of their fertility levels. The critical value of this proportion is 0.25 and 0.35, respectively, for the typical brown earth and brown earth type paddy soil, i. e., the soil fertility is higher if the value is less, or otherwise. Soil improvement measures could decrease the compositional proportion of soil characteristic microaggregates, and increase the soil fertility.