The changes in size, activity and structure of soil microbial community caused by N fertilization were studied in a laboratory incubation experiment. The rates of N fertiliser applied (KNO3) were 0 (control), 100 and 2,000 ?g N g-1 soil. Despite no extra C sources added, a high percentage of N was immobilized. Whereas no significant increase of microbial C was revealed during incubation period, microbial growth kinetics as determined by the substrate-induced growth-response method demonstrated a significant decrease in the specific growth rate of microbial community in soil treated with 2,000 ?g N g-1 soil. Additionally, a shift in microbial community structure resulting in an increase in fungal biomarkers, mainly in the treatment with 2,000 ?g N g-1 soil was visible.