This study was designed to examine the effects of continuous fertilization, straw incorporation, and manuring on the soil microbial biomass and activities of enzymes by a long-term fertilizer field trial with winter wheat and summer maize rotation system under temperate conditions in a loess soil in Shaanxi of China. Treatments at the site included application of recommended doses of nitrogen (N), nitrogen and phosphorus (NP), nitrogen, phosphorus and potassium (NPK), wheat/maize straw (S) with NPK (SNPK), dairy manure (M) with NPK (MNPK) and un-amended control (CK), totally six treatments. The results showed that soil microbial biomass carbon and nitrogen changed significantly during maize growing season. The effects of fertilization regimes on soil microbial biomass carbon and nitrogen can be arranged (based on statistical significance) in the following orders: MNPK > SNPK, NP, NPK > N, CK. Soil enzyme activities also significantly changed with maize development stage. Invertse, urease and cellulase activities reached the peak at the silk stage, but alkaline phosphatase activities was the highest at the jonting stage. The effects of fertilization regimes on soil enzyme activity generally followed the order: MNPK > SNPK > NPK, NP > N, CK. The difference in soil microbial biomass carbon, nitrogen and enzyme activity was related to the levels of organic carbon, total nitrogen and Olsen P in soils. Overall, long-term application of NP or NPK could significantly increase soil microbial biomass carbon, nitrogen and enzyme activity relative to CK. Compared with NPK, SNPK treated soil had a tendency to increase microbial biomass and enzyme activity. At the same N application rate, manure combined with chemical fertilizer significantly enhanced soil chemical and biochemical fertility compared with the other fertilization regimes. It is, therefore, recommended that NP application combined with crop straw could be a suitable way in the loess soil in order to improve soil fertility and maintain land productivity if organic manure were not applicable.