New candidate targets, biological mechanisms as well as small-molecules are significant factors in the research and development of first-in-class drugs, which is a challenging process with a large amount of time and money devoted as well as high risks. A successful first-in-class drug can not only become a new strategy for disease treatment but can also offer innovative research ideas for the design of drugs. The Food and Drug Administration (FDA) approved 48 new drugs to the market in 2019, among which small-molecule drugs still predominated, containing several first-in-class drugs. Brexanolone, for example, is the first positive modulator of GABA_A receptor for the treatment of postpartum depression; Selinexor is the first small-molecule drug to treat recurrent refractory multiple myeloma by inhibiting exportin (XPO1); Tenapanor is the first sodium/proton exchanger type 3 (NHE3) inhibitor that can treat irritable bowel syndrome; Lasmiditan is the first approved agonist with selectivity for 5-HT_1F, treating migraines. The research and development processes of the first-in-class drugs mentioned above are distinctive from each other with uniqueness and innovation. In this review, we briefly analyze the background and process of the research and development of three typical cases as well as their therapeutic applications in an attempt to offer some help for the future development of first-in-class drugs.