Ribociclib is an oral small molecule cyclindependent kinase 4/6 inhibitor,which inhibits tumor progression by inhibiting the conversion of tumorcells from G1 phase to S phase.The combination ofribociclib and letrozole was approved in the United States on March 13,2017 as a treatment for HR+/HER2-advanced and metastatic breast cancerpatients.Clinical results showed that the drug on advanced and metastatic tumors had a significant inhibitory effect and could extend the survival of patients without deterioration compared with using letrozole alone.The incidence of adverse drug reactions is higher,but the tolerance is better.This article focuses on pharmacodynamics,pharmacokinetic,clinical results and adverse effects of this drug.