Reliability and behaviour of composite columns is influenced by many factors. This paper presents a comparative study of the reliability and performance of square composite columns under axial compression, taking into account mechanical and geometric variability. The choice is opted for metal hollow profiles filled with ordinary concrete and high-performance concrete. In this study, a mechanic-reliability model to calculate the reliability index and the probability of failure of different columns is presented. The response surface method is used to accomplish this coupling in order to describe the uncertainties in a suitable model and to study their influence for a reliability assessment. The results show that the material and geometric characteristics of the columns have a significant influence on strength and reliability. The sensitivity of the random parameters of structural reliability is assessed from the proposed method.