Abstract: The major challenge in the development of recombinant biologics lies in generating and isolating rare high-producing stable single clone in a short period of time. The selection marker is an essential component of the plasmid vector, it plays an important part in the generation and screening of producing cell lines. Engineering the selection marker to enhance the stringency of selection for high producing cells is one of the most effective approaches to improve the cell line development process. Here, using Chinese hamaster overy (CHO) cells as an example, we introduce the application of selection marker for generation of recombinant biologics producing mammalian cell lines, methods of engineering the selection markers to enhance the selection stringency, and propose considerations on cell substrate stability and selection marker safety, in order to provide references for high-efficiency development of recombinant biologics.