We studied in the laboratory the effects of adding Wheat Straw Chopped (WSC) and No Chopped (WSNC) and with and without urea (150 kg N ha^-1) (WSC+N and WSNC+N) on soil biochemical properties of a Typic Xerofluvent. Materials were transferred into the microcosms 24 h after application and triplicate treatments were incubated in darkness at 25 °C inside an incubation chamber for seven lengths of time (3, 7, 15, 30, 60, 90 and 120 days). Soil microbial biomass, and the activities of urease, dehydrogenase, protease-BBA, &beta-glucosidase, and alkaline phosphatase were measured in soils for each time of incubation. The results obtained indicate the importance of the application wheat straw chopped with N respect to the rest of fertilizer treatments studied. In this respect, and at the end of experimental period, soil microbial biomass increased 21% in WSC treatment respect to WSNC treatment, 24.2% in WSC+N treatment respect to WSC treatment, and 39% in WSNC+N treatment respect to WSNC treatment. As regards the soil enzymatic activities analyzed, the highest values at the end of experimental period were observed in WSC+N-amended soils, followed by WSNC+N-amended soils, WSC-amended soils and WSNC-amended soils.