摘要：UV irradiation hydrogen peroxide ( $$\hbox {H}_{2} \hbox {O}_{2}$$ ) system is used as an effective, easy and low-cost combined depolymerization technique to produce oligosaccharides from chitosan. UV–Vis spectroscopic studies explained that with increasing treatment time, the absorption of the depolymerized chitosan solution has increased, indicating the increase in the carbonyl and amino groups in their structure. Fourier transform infrared spectroscopy and nuclear magnetic resonance (1H NMR) analysis showed that the 1,4- $$\beta $$ -d-glucoside linkages of chitosan are degraded without important changes in chemical structure of decomposed samples. X-ray diffraction patterns verified the polymerization of chitosan to produce oligomers, changing in structure from crystalline to amorphous. Viscosity-average molecular weight measurements of fragmented chitosan samples and Mark–Houwink equation are used to demonstrate the efficiency of this depolymerization method. Finally, the obtained results ascertained that this combined method could produce water soluble chitosan with significant efficiency and no essential change in its chemical structure.