Multiple myeloma (MM) is the most common cause of death from hematological malignancy worldwide, and recent studies have revealed that let-7b-5p can play an inhibitory role in tumorigenesis. However, the role of let-7b-5p in MM still remains unclear. The aim of this study was to elucidate the molecular mechanisms by which let-7b-5p acts as a tumor suppressor in MM. Here, quantitative real-time polymerase chain reaction results showed that the expression of let-7b-5p was remarkably reduced in MM tissues and MM cell lines (RPMI-8226 and U266 cells). Furthermore, over-expression of let-7b-5p significantly suppressed RPMI-8226 cell proliferation and induced S/G2 cell cycle arrest and apoptosis. Luciferase reporter assay results demonstrated that insulin-like growth factor receptor 1 (IGF1R) was negatively regulated by let-7b-5p at the post-transcriptional level VSports手机版. The mRNA and protein levels of IGF1R in RPMI-8226 cells were down-regulated by let-7b-5p. Furthermore, the cell phenotype altered by let-7b-5p inhibitor can be rescued by IGF1R silencing (si-IGF1R). Taken together, our results demonstrated that let-7b-5p functions as a tumor suppressor in MM, suggesting that let-7b-5p may be a potential therapeutic target for MM. .