<p>As promising stabilizing additives, nano-additives, when combined with inorganic stabilizing additives for soil stabilization, demonstrate increasing potential for engineering applications. This study presents a laboratory-scale assessment of clay stabilization using nanosilica and nano-calcium carbonate through a series of unconfined compressive strength, ultrasonic pulse velocity, and microstructural tests. The results indicate that the incorporation of either nano-additives leads to improvements in the unconfined compressive strength and ultrasonic pulse velocity of the stabilized clay compared to ordinary cement stabilization, with the optimal proportions determined to be 3% for nanosilica and 2% for nano-calcium carbonate. Notably, the addition of nanosilica is more effective in enhancing mechanical performance, exhibiting strength enhancement of 145% and 115% after 28 and 60 days of curing, respectively, at the optimal dosage, compared with the ordinary cemented specimen. Microstructural observations align with these findings, revealing that nanosilica leads to a denser matrix and more uniform pore distribution, whereas only limited pore-structure refinement is observed with nano-calcium carbonate. Furthermore, both unconfined compressive strength and secant modulus exhibit unique exponential correlations with ultrasonic pulse velocity across various stabilization series, irrespective of curing time. These relationships support the feasibility of using ultrasonic velocity as a reliable non-destructive method for predicting strength development and stiffness evolution, providing practical guidance for both laboratory-scale mix optimization and the preliminary design of nano-additives in clay stabilization.</p>