In this study, by gene knockout with CRISPR/Cas9 gene editing technique, we determined the regulation of CDK4 or CDK6 on ABCB1-mediated MDR in human epidermoid carcinoma MDR cell line KB-C2 which overexpresses ABCB1 and H460/MX80 which expresses ABCB1 at low level. Here, ABCB1 is linked to squamous cell carcinoma.