The content of organic carbon in atmospheric aerosol was determined in the aerosol samples collected at two sites in Southwestern Siberia and at three sites in Northwestern Siberia. According to many-year observations, the mean mass concentration of the submicron fraction of atmospheric aerosol at the sampling sites in Southwestern Siberia is about 16 mg/m3. The averaged data on the organic carbon concentration in the samples from Klyuchi and Karasuk for the period since January 2000 until October 2002 give the value of 2.7 mg/m3. The fraction of the ozone reactions in oxidation of hydrocarbons leading to generation of the aerosol mass of organic carbon was estimated to be up to 20%. For the sampling sites in Southwestern Siberia, no tendency is observed in the dependence of the standard deviation on the concentration. At the sampling sites located in the Northwestern Siberia, the lower is the measured carbon concentration the higher is nonuniformity (fluctuations) in the data set. For this reason one can conclude that for the northern territories the major contribution to the organic carbon mass is due to the long-range transport, while local sources play a less significant role. For the southern regions, the situation is quite different, and this suggests that just these latitudes form the global/regional background, which affects the northern territories.