The main objective of this study was to determine changes in microbial response in natural soil aggregates for soil characterization in different fluvial land shapes. This study was carried out in fluvial lands formed on accumulated sediment depositions carried by Kizilirmak River. The majority soils of the study area were classified as Typic Ustifluvent and Typic Haplustept in Soil Taxonomy. It was found that macroaggregates (especially >6300 mu m and 20004750 mu m diameters) of all soil samples were higher than microaggregate of soils. In addition, it was determined that the Corg content varies between 0.410.91% in soil samples. Cmic content was also found higher level in aggregates involved <250 and 250425 mu m diameters as compared to other aggregate size classes. Moreover, we detected that Corg:Cmic ratio was much higher in macroaggregates than in microaggregate fractions. BR levels were also greater in macroaggregates of >6,300, 4,7506,300 and 2,0004,750 mu m than in the other macroaggregates sizes and microaggregates. Consequently, macroaggregates have relatively more Corg level than the Corg level in microaggregates, even if the absolute values of Cmic were the lower. This study thus evidenced contrasting microbial habitats and their response in different soil aggregate size formed in various developed soils.