Change of soil quality in the black soil zone of north-eastern China is shown by soil biological properties such as soil microbial biomass, soil respiration and enzyme activity under different long-term fertilisation. This study was conducted to disclose the relationship between soil fertility and soil microbial properties based on long-term fertilisation field experiments. The results showed that the activity of β-glucosidase has a significantly (P < 0.01) positive relationship with urease activity, and has a negative (P < 0.05) relationship with activities of alkaline phosphatase and acid phosphatase. The correlation coefficients showed that the activities of β-glucosidase and urease were significantly (P < 0.05) positively correlated with total carbon, total nitrogen contents and available nitrogen contents of the soil. Activities of acid phosphatase and alkaline phosphatase showed a significantly (P < 0.05) negative correlation with soil total nitrogen and soil pH.