A dicistronic expression vector was constructed for Chinese hamster ovary (CHO) cells that produce both selectable marker-DHFR (dihydrofolate reductase) gene and recombinant antibody cDNA from a single primary transcript via differential splicing. The vector was derived from a pDHL vector and contained the human constant region cDNA so that any human-mouse chimeric antibodies could be expressed. The expression vector produced stable CHO cell clones that secreted nearly double the amount of chimeric antibodies than produced by conventional expression approaches, where the DHFR gene and relevant cDNA are controlled by separate transcription cassettes. Clones with increased expression of interested genes can be efficiently generated by selection in medium containing a gradually increasing amount of methotrexate. The dicistronic expression system using incomplete splicing DHFR gene strategy thus provides a convenient, high-level, and rapid expression of chimeric antibodies.