Use of industrial by-products to improve subgrade soils in flexible pavements is gaining popularity as a sustainable construction practice. Calcium carbide residue (CCR) is a by-product of acetylene gas industry. In this paper, an attempt has been made to evaluate the influence of calcium carbide residue in improving the performance of clayey subgrade soils. The improvement in resilient modulus of two clayey soils (with low plasticity and high plasticity) with the addition of calcium carbide residue is studied by carrying out repeated load triaxial tests. The influence of variation in moisture content on the repeated loading behaviour of virgin soils and CCR stabilized soils is examined. Two regression models (Universal and NCHRP model) reported in literature are found to exhibit very good fit with the experimental data. © 2018 Informa UK Limited, trading as Taylor & Francis Group.