This paper presents a theoretical analysis for rectangular hollow section (RHS) tapered columns in order to define the elastic critical buckling loads of the columns subjected to uniform compressive stresses. The critical buckling load of (RHS) tapered column is affected by the buckling coefficient of plate elements which is a function of the type of loading, edge support conditions, the plate aspect ratio, and the tapering ratio. A simple and convenient method is proposed using the energy method in order to formulate the necessary equations, which takes into consideration the web-flange interaction and effect of tapering ratio of web on the buckling coefficient of the section. The results are represented diagrammatically as function of the ratio of buckling load to average area yield load with respect to the different mentioned ratios. A comparison between the buckling coefficient as obtained by the energy method and the finite element method through ANSYS program is also performed.