This study is to assess the spatial and seasonal soil microbial biomass variation in Algerian steppe soils using the fumigation extraction method. The microbial biomass carbon ranged from 78 mg.kg-1 dry soil to 245 mg.kg-1 dry soil with an average of 146 mg.kg-1 dry soil; forming an 1,5% of total soil organic carbon. The soil microbial biomass carbon dynamics depends on the seasonal climatic conditions; the highest values were recorded in spring and autumn, while the lowest values were noted in winter and summer. The summer desiccation has a much greater influence on the reduction of microbial biomass carbon than the winter freeze. The sampling date is a key factor to assess the critical threshold of microbial biomass in these ecosystems.