A high-molar-mass hyaluronan (HA) was exposed to oxidative degradation by Cu(II) ions and ascorbate. It is the so-called Weissberger biogenic oxidative system (WBOS), which mimics the acute phase of joint inflammation. Oxidative degradation of HA was examined by rotational viscometry, where the decrease of dynamic viscosity of the HA solutions by WBOS itself [1] or in the presence of herbal extracts such as Agrimonia herba, Cynare folium and Ligustri folium was monitored. The order of added substances to the HA solution were: 1) Cu(II), herbal extracts followed by ascorbate as an inducer of free radical degradation (production of ^●OH radicals), 2) Cu(II), ascorbate followed by herbal extracts with a 1 h delay (production of peroxyl radicals). The results of rotational viscometry showed that the most effective scavengers of ^●OH and peroxyl radical were Agrimonia herba and Cynare folium, respectively. The results of the ABTS and DPPH assay demonstrated the highest radical scavenging capacity of Agrimonia herba.