Abstract: Molecular farming in plants has a lot of advantages as they are inexpensive, safe and convenient. In clinical trials, several plant-derived pharmaceutical proteins, such as antibodies, vaccine antigens, and cytokines have been found to induce a high immune response. However, only a few small-scale products have so far reached to the market. The problems of low yield and poor immunogenicity are the two major challenges that militate against the full exploitation of plant’s expression system. Strategies have been developed to break through these barriers which focus on the choice of suitable host plant, vector optimization, and the use of mucosal adjuvants. This article reviews the different novel plant-derived pharmaceutical proteins, the limiting issues, and discusses the technologies and strategies to assess the development trends of plant molecular farming.