Nano-treatment is a budding technique used for enhancing the engineering characteristics of clayey soils. Different types of nanomaterials are employed by researchers in various soils to understand the impact of nano-treatment on soil behaviour. This study investigates the efficacy of nano-calcium carbonate in improving the strength and compressibility properties of three distinct clayey soils dominated by illite, montmorillonite, and kaolinite as their primary clay minerals. The addition of optimal amounts of nanomaterial significantly enhanced the strength and reduced the compressibility of various clays, even within the first week of treatment. The performance of nano-treated clays also depends on the soil pH, clay mineralogical composition, and the morphological characteristics of the nanomaterial. The microstructural examinations revealed that the invasion of nano ions into the layered clay structure led to their transformation into a nanocrystalline state.