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Globally about 23 % of the dry lands are affected by soil degradation due to lack of soil organic carbon (SOC). Increasing temperature and artificial stress of various management practices including tillage accelerate soil aggregate breakdown and increase the loss of soil organic carbon to the atmosphere. This study was conducted for comparing SOC fraction in different land use and soil management types in arid soils of Rajasthan and to study the effects of temperature fluctuation on soil organic carbon fraction dynamics. In the experiment two temperature regimes were maintained; ambient and elevated (ambient + 40 A degrees C). All the soil organic carbon fractions were analyzed and it was revealed that soil organic carbon fractions were more under trees (0.33 %) compared to grass (0.23 %) land use system. The mean soil microbial biomass carbon (SMBC) and dehydrogenase activity under trees were 13.9 A mu g C/g soil, 3.2 pkat/g and under grasses were 10.8 A mu g C/g soil, 2.0 pkat/g respectively. The SOC content under temperature fluctuated samples were about 18 % higher than the control samples. Overall increasing temperature to about 45 A degrees C reduced the SMBC to an extent of 19 % compared to room temperature and the dehydrogenase activity was about 9 % lower than room temperature.