Abstract The reinforced concrete columns are, in general, subject to a law of non-uniform bending moment due to the existence of unequal end eccentricities. In addition, the use of high-strength concrete in the construction of ordinary structures is becoming increasingly common, which suppose the design of more slender columns. However, the literature review indicated that experimental studies for high-strength concrete columns subjected to different end eccentricities are scarce and focus their study on the behavior of short-length columns under one way flexural-compression loadings. On the other hand, the design codes generally propose simplified methods in order to predict the ultimate load of slender columns under compression with unequal end eccentricities. However, the simplified methods have been verified, in most, with normal strength concrete columns. The extrapolation of these methods to high-strength concrete without scientific support and adequate experimental verification may lead to unreliable results. The behavior of 68 slender columns under compression with different end eccentricities and skew angles cast with normal and high-strength concrete has been studied on this thesis. These experimental tests are aimed at understanding the behavior of this type of structural elements and also should serve to calibrate numerical models and to validate simplified methods. The research importance focuses on the contribution of increasing the available experimental database in order to verify the design methods proposed by the different design codes for reinforced concrete columns subjected to this kind of solicitation. In addition, a parametric study was conducted to propose an expression for calculating the coefficient of equivalence Cm, taking into account the behavior of such structural elements, through a numerical finite element method calibrated with the experimental data. The proposed expression covers the normal and high-strength concrete slender flexural- compression columns under unequal eccentricities and skew angle loaded ends.