The article presents a comparative analysis of an optimal design for conventional and geothermal energy piles, based on mixed-integer and non-linear programming (MINLP) optimizations. To complete this analysis, a MINLP optimization model OPTPILE was constructed. The model is based on structure production costs, while the piles are made of more than one material. It was subjected to geotechnical designs, structural resistance and settlement constraints that satisfy the requirements of the ultimate and serviceability limit states of the Eurocode specifications and recommendations for design and analysis of geothermal energy piles. The optimal design of a conventional and geothermal energy pile was investigated for various soil and load conditions. A comparative analysis of MINLP optimizations were performed over a wide range of alternative scenarios: different vertical loads on the pile, alternatives of discrete cross-sections as well as different Young's moduli of the soil. Based on the calculated results, a recommended optimal design for a conventional pile and a geothermal energy pile were developed. (C) 2018 Elsevier Ltd. All rights reserved.