Purpose <p>Ordinary Portland cement-sulphoaluminate cement (CSC) with mass ratio of 1:1 was used to stabilize dredged sediments (DS) containing humic acid (HA), and nano-modification was adopted to further improve the stabilization efficiency. A series of strength and microstructural tests were conducted to clarify the strength development and associated micro-mechanisms of CSC-stabilized DS (CSDS).</p> Methods <p>Three types of nanoparticles including nano-SiO₂ (NS), nano-MgO (NM), and nano-Al₂O₃ (NA) were incorporated as nano-modifiers in single and composite forms. Unconfined compressive strength (UCS) tests were conducted to investigate the strength development of nano-modified CSDS under effects of CSC content, HA content, water content and nano-modification. X-ray diffraction (XRD), thermogravimetry (TG), and scanning electron microscopy (SEM) tests were also performed to clarify the micro-mechanisms affecting the strength development of nano-modified CSDS.</p> Results <p>Incorporating suitable nanoparticles can significantly improve the strength-gaining properties of CSDS, and optimum dosages of single NS, NM, and NA were respectively 4%, 5%, and 4%. Compared with single nano-modification, the composite nano-modifier NS/NA with mass ratio of 3:7 exhibited the best efficiency. Adding 4% optimum NS/NA can improve the 7d-, 28d-, and 90d-UCS of CSDS by 25.2%, 31.4%, and 31.4%, respectively. The cementitious products C-S-H gel, C-A-H gel, and ettringite were mainly responsible for the strength development of nano-modified CSDS.</p> Conclusions <p>Nano-modification is an effective approach to improve the stabilization efficiency of CSC on DS containing HA, and composite nano-modifier NS/NA with mass ratio of 3:7 exhibited best efficiency.</p>