This study was done to assess the effects of Urtica dioica, Plantago major and Hypericum perforatum L herbal mixture in the MCIA rat model. In addition, a new pathological and clinical arthritis lesion assessment was developed. Sprague-Dawley (SD) rats were immunized with bovine type II collagen and muramyl dipeptide (MDP). Commercial herbal extracts were administered daily to the rats after the immunization for the course of experiment (90 days). Rats were boosted with a second collagen-MDP emulsion 60 days after the first immunization. Paws were daily evaluated macroscopically for redness, swelling, distortion, or ankylosis of the joints. On the day of sacrifice, rat paws were assessed for histopathologic changes. Herbal mixture administration decreased the clinical lesion manifestation in the MCIA rat model and led to development of similar or slightly more severe histopathological lesions compared to rats that did not receive the treatment. The clinical arthritis signs appeared as early as 13 days after the first MDP/collagen injection and with peak incidence at 20 days post-immunization. Histopathologically, animals showed changes ranging from mild to very severe. Administration of the herbal mixture used in this study had a clinical therapeutic effect on the course of the clinical manifestations in the MCIA model, but the herbal treatment had no such effect on the histopathological lesion development and even led to slightly more severe lesions. Rats in the MCIA model developed prominent clinical and histopathological changes that were comparable to rheumatoid arthritis (RA) lesions in humans.