Carrageenan application in the biomedical field is influenced by the size of molecular weight. Depolymerization process is needed for changing the high molecular weight (HMW) fraction of κ- carrageenan into low molecular weight fraction (LMW) of κ- carrageenan. Ozone is a powerful oxidant and considered for depolymerization of κ- carrageenan. This research was conducted as an investigation on the influence of the combination of ozonation and ultrasonication (OZ/US) on the chemical and morphological characteristics of κ-carrageenan. FTIR and Scanning electron microscopy (SEM) was used to determine the change of chemical and morphological characteristics of κ-carrageenan. The result of this study showed that there was no change of chemical properties of κ-carrageenan during OZ/US treatment. The sulfate content was obtained after OZ/US treatment tends to be stable.  Nevertheless, the result of SEM analysis showed that there were changes on morphological characteristics of κ-carrageenan after OZ/US treatment.  Keywords: ultrasonication, κ-carrageenan, ozonation, morphological, chemical