In recent years, more and more attention has been drawn to the research on the association of micro ribonucleic acid(miRNA) with diseases using gene-chip technology. miRNA-21, a member of the miRNA family, has many biological functions and has been proven to be associated with the occurrence and development of a good number of diseases. Studies have suggested that miRNA-21 can be used as a biomarker for the progression of lung cancer, providing a possibility for early intervention in the progression of lung cancer. This paper reviewed the recent progress made in the research on miRNA-21 and lung cancer.