Based on the measurements of soil nutrients and microbe and canonical correspondence analysis of them,the paper aimed to reveal the relationships between soil nutrients and microbe in Eucalyptus urophylla×E.grandis plantations with different ages in southeastern Guangxi,China.The results indicated that:(1)The effect of stand ages on available phosphorus and pH were not significant,while that on other indexes differed greatly.Soil organic matter(SOM),total nitrogen(TN),total potassium(TK),and available nitrogen(AN) basically increased firstly and then decreased,and the details about peaks differed.(2)The effects of stand ages on the sum of soil microbial population,bacterium,fungi,and actinomycetes were evident:the sum of soil microbial population,population of bacterium,fungi,and actinomycetes had higher values in 3a and 8a stand plantations;the variation trend of bacterium was increasing firstly,and then decreasing,and finally increasing,which was identical with fungi,while the variation trend of actinomycetes was not evident;bacterium accounted for most percentage parts in the sum of microbial population,followed by actinomycetes and fungi.(3)All the affection of stand aging on soil microbial biomass of carbon(C_mic),nitrogen(N_mic),and phosphorus(P_mic) was distinct.The variation of C_mic performed in a broken-line manner,peaked at 8a plantation and followed by at 1a plantation;that of N_mic presented in a “V” shape,peaking at 1a and 8a plantations and lowest value existing in 3a plantation;the variation of P_mic was opposite to N_mic,peaking at 5a plantation and lowest values occurring in 1a and 8a plantations.(4)Canonical correspondence analysis showed that most of the relationships between soil main nutrients and soil microbes were not positive or not-significant.This indicated that soil main nutrients,soil microbe as well as the relation between them was not only affected by stand age,but also influenced by the topography factors.