Chitosan Oligosaccharide (COS) nanoparticles prepared by ionotropic gelation method using sodium tripolyphosphate (Na-TPP) coated with Hyaluronic acid (HA). The coating confers biological advantage to the nanoparticles in terms improved circulation time in the plasma and targeting ability. This nanoparticulate system has potential application in targeted nucleic acid delivery as they can be tuned to possess overall cationic properties for binding anionic nucleic acids. In the present investigation, we studied the effect of COS of varying molecular weights on the formation COS-TPP nanoparticles coated with HA. Amongst them, COS with higher molecular weight resulted in formation of stable nanoparticles, along with TPP and HA. We also investigated the influence of molecular weight of COS on their physicochemical properties, in particular, the ability to form nanoparticles with a narrow-size distribution. Furthermore, computational studies were conducted to understand molecular mechanism, which revealed that protonation modulates the behaviour of COS during formation of stable nanoparticles. (C) 2016 Elsevier Ltd. All rights reserved.