Cancer is one of the leading causes of death worldwide. There is a definite need for novel approaches to improve the diagnostics and treatment of cancers. The pathological processes leading to carcinoma are associated with the altered expression of a specific gene relevant to malignancy. MicroRNA-125b (miR-125b) is a small non-coding, multipurpose miRNA that plays a key role in several different biological processes. Increasing amounts of evidence indicates that miR-125b may serve as a diagnostic biomarker of certain kinds of cancers. miR-125b may be suitable to be used as a therapeutical target in several human diseases including neoplastic disease. Here, we review the latest progress in the identification and validation of the relationship between cancer-related miR-125b and cancers, and discuss the functions of miR-125b that regulates many processes of diseases, including cell proliferation, differentiation, and apoptosis.