Let-7g miRNAs, short non-coding RNAs approximately 21 nucleotides long, repress protein translation by binding to the 3'UTR of target mRNAs. Aberrant expression of let-7g is associated with the poor prognosis of lung cancer patients. Compared to normal lung cells, let-7g expression is absent in non-small cell lung cancer (NSCLC) cells. Furthermore, K-Ras and HMGA2 are well known as targets of let-7g. In this study, we evaluated the potential role of precursor (pre)-let-7g in lung cancer cell metastasis, focusing on the two targets of let-7g, HMGA2 and K-Ras. We found that pre-let-7g inhibited the migration of A549 lung cancer cells through HMGA2-mediated E2F1 down-regulation. Thus, our results suggest that pre-let-7g could be used as a suitable target for the suppression of lung cancer cell migration.