The effectiveness of the treatment strategies for Parkinson’s disease (PD) is highly dependent on the time of therapeutic intervention. This makes early diagnosis of PD an essential factor for its treatment; however, the complexities of the symptoms make it difficult to diagnose at an early stage. Moreover, by the time the symptoms start to appear, the disease has already been propagated in the patients. Even for the researchers, it is difficult to understand the important early diagnostic biomarkers due to the unavailability of the patients at the early stage, that is, before the manifestation of visible symptoms. The solution to this problem appears to develop animal models and monitor them from the early days to discover the diagnostic biomarkers. In this chapter, we shall discuss the use of animal models in the research intended to discover early diagnostic biomarkers for PD and why it is important to use animal models.