In this work, we report the effect of thermal stability of various capping ligands in modified digestive ripening (MDR) technique for probing the mechanism of formation of self-assembled monodipserse Cu nanoparticles from the polydisperse Cu nanoparticles. Narrowing of the size distribution of monodisperse Cu nanoparticles after modified digestive ripening process is strongly dependent on the thermal stability of capping ligands. Various capping ligands such as dodecanethiol (DDT), octadecanethiol (ODT) and mixture of DDT and ODT are successfully used in modified digestive ripening method and performed the process at various temperatures (60, 120 and 180 °C) to study the effect of thermal stability of these ligands on the size and self-assembly of cu nanoparticles. Using DDT as capping ligand, decrease in particles size and monodispersity observed at 60 °C and complete monodispersity is achieved after 120 °C due to low thermal stability of DDT. However, with ODT and multi ligands, complete monodispersity is achieved at 180 °C due to high thermal stability of ODT as compared to DDT. © 2019 Elsevier B.V.