B-cell translocation gene 2 (BTG2), the first gene identified in the BTG/TOB gene family, is involved in many biological activities in cancer cells acting as a tumor suppressor. The BTG2 expression is downregulated in many human cancers. It is an instantaneous early response gene and plays important roles in cell differentiation, proliferation, DNA damage repair, and apoptosis in cancer cells. Moreover, BTG2 is regulated by many factors involving different signal pathways. However, the regulatory mechanism of BTG2 is largely unknown. Recently, the relationship between microRNAs and BTG2 has attracted much attention. MicroRNA-21 (miR-21) has been found to regulate BTG2 gene during carcinogenesis. In this review, we summarize the latest findings in the investigations of biological functions of BTG2 and regulation of its expression, with an emphasis on miR-21 in regulation of BTG2 gene in various cancers. B-cell translocation gene 2 (BTG2), also known as PC3 or TIS21, belongs to the antiproliferative (APRO) gene family. Several studies have demonstrated that BTG2 is involved in a large number of physiological and pathological processes, such as cell differentiation, proliferation, apoptosis, and other cellular functions, acting as a tumor suppressor. In this review, we summarize the latest findings in BTG2 studies, highlighting the mechanisms for the regulatory effects of microRNAs (miRNAs) on BTG2 gene expression in the most common human cancers.