The effects of two plantation stands of non-N-fixing Castanopsis hystrix and N-fixing Erythrophleum fordii on soil microbial biomass and microbial community structure in south subtropical China were studied by fumigation-extraction and phospholipid fatty acid (PLFA) analyses. The results showed that soil pH, soil N status (total N, NH₄⁺-N and NO₃^--N), soil microbial total PLFAs, bacterial PLFAs, actinomycetes PLFAs and arbuscular mycorrhizal fungi PFLAs were significantly influenced by plantation type and season, while only season significantly influenced soil microbial biomass carbon and fungal PLFAs, but soil microbial biomass nitrogen(MBN) was not significantly affected by plantation type and season. The content of soil NH₄⁺-N and NO₃^--N in C. hystrix plantation were significantly higher than those in E. fordii plantation during both the dry and rainy seasons. In addition, the amounts of soil microbial total PLFAs and bacterial, actinomycete, and arbuscular mycorrhizal fungi PFLAs in C. hystrix plantation were significantly higher than those in E. fordii plantation during both the seasons as well. Furthermore, the richness and Shannon diversity index of soil microbial PLFAs were significantly altered by plantation type, Shannon diversity index of soil microbial PLFAs in C. hystrix plantation was significantly higher than that in E. fordii plantation during both the seasons. Principal component analysis indicated that variations in the soil microbial community structure were affected by both the plantation types and seasons. Redundancy analysis of soil microbial community structure and environmental factors showed that NO₃^-, soil water content, soil pH, and microbial biomass nitrogen had significant correlations with PLFA signatures. Thus, our study results showed significantly different effects of non-N-fixing C. hystrix and N-fixing E. fordii plantation stands on the soil microbial biomass and community structure. Overall, soil pH and N status may be the main factors that could regulate soil microbial biomass and community structure in the studied plantations.