Biosimilar is a topic of much debate, not only among pharm and biotech companies, but also major regulatory bodies such as US FDA and the European Medicines Agency. The traditional classic chemical synthesized generic drug was introduced with only limited data needed for market approval, which, however, cannot be extrapolated to biologics. The technical know how required to develop biologics and follow-ons is undoubtedly greater than that of small molecule chemical drugs. In the biologics scenarios, the comparability of efficacy and safety from the clinical trials, and the comparability of pharmacokinetics and pharmacodynamics parameters are the key for the success of follow-on biologics. There are tremendous both scientific and statistical challenges in developing follow-on biologics. In this talk, we discuss some scientific and statistical challenges in developing follow-on Biologics.