Composite section has been used for many advantages than using steel or reinforced concrete alone. The main advantages of composite sections are enhancing the capacity of section, prevent local buckling, reduce the general buckling, achieve greater stiffness, resist fire, ... etc. Composite sections have been widely used in high towers and skyscrapers. For the factories and industrial buildings, steel structures only may be used. Civil defense regulations require using high cost special paintings for fire resistance, or the other solution is to cover the lower part with a thick layer of reinforced concrete. We can treat this part of the column as a composite section. This will result in what we can name a partial composite column. Most of the current design codes don't mention the behavior of this system (partial composite column) due to the lack of both experimental data and practical experience. Therefore this paper studies the behavior and the critical buckling load of such systems using Sap 2000 v11.04 finite element modeling software.