The specifically expressed genes (SEGs) only expressed in unique or a small number of tissues/conditions provide important clues about the gene and tissue-specific biological functions. SEGs may serve as potential biomarkers for disease diagnosis and treatment. The identification of SEGs will be helpful to globally and dynamically understand the gene functions and their roles in biological processes. However, the mechanisms of their specifically high or low expression remain to be revealed and explained urgently. SEGreg is a comprehensive database containing SEGs identified by our SEGtool from four high-throughput datasets of different cancers/tissues/cell lines (TCGA, BodyMap, CCLE and GTEx), along with their corresponding miRNA and TF regulations collected from several databases. SEGreg will provide useful clues to reveal the functions and regulations of SEGs.