This chapter introduces some types of animal models which are used for better understanding the disease mechanisms and its treatment. These experimental models fall into two categories: spontaneous models and induced models. Among the diseases, rheumatoid arthritis (RA) as an autoimmune disease was considered. To study the pathogenesis of RA, we explained collagen-induced arthritis as an animal model that reflects a characteristic feature of RA patients. In addition, experimental allergic encephalomyelitis (EAE) as an experimental model for multiple sclerosis (MS) was explained in detail to represent a standard method to investigate in its mechanism, finding the way for the amelioration of this incurable neurological disorder.