Similar biological medicinal products should demonstrate similarity to the already authorized product (reference product) in terms of quality, safety and efficacy. Due to the high complexity of biological medicinal products, the standard generic approach (bioequivalence) which is applicable to most chemically-derived medicinal products is in principle not appropriate to biological-derived products. Limited by technologies, we are not able to identify the two biological medicinal products are "equivalent", we can only conclude that they are "similar". Based on clinical points of view, the author explained the biosimilar concept, summarized biosimilar guidelines from US FDA, EMA and Taiwan, and provided the first authorized biosimilar product in Taiwan (Omnitrope) as an example.