Abstract: In this paper the effects of long-term (15 years) combined application of inorganic and organic fertilizers on soil microbiological properties and soil fertility was carried out based on the long-term fertilizer experiments in Fluvo-aquic soil in Changping County, Beijing, China. The main results are as follows: Long-term application of chemical fertilizers only (NPK) compared with long-term no fertilizer usage (CK) increased the soil microbial biomass of C (SMBC) &N (SMBN), SMBC/SOC (soil organic C), SMBC/SMBN, Urease activity, and soil organic matter (SOM), soil total nitrogen (STN) and soil total phosphorus (STP) in a certain degree. Combined application of inorganic fertilizers (NPK) and organic manure or crop straw can have even more significant increase effects on above related soil and microbiological properties than long-term applying NPK fertilizer only. The more the application amounts of organic manure or crop straw, the more significant the increase effects of above related soil and microbiological properties. Meantime long-term application of organic manure or crop straw can slightly decrease the soil pH under alkaline Fluvo-aquic soil (the pH around 8.00 in this experimental soil). A positive co relationship was found between soil microbial biomass of C (SMBC) &N (SMBN), Urease activity and soil organic matter (SOM), soil total nitrogen (STN) and soil total phosphorus (STP) .