As an efficient tool that has been developed recently, serial analysis of gene expression (SAGE) allows the qualitative and quantitative analysis of a large number of transcripts. It can define the transcripts at relatively low levels and characterize the genomic expression near completion. In addition, it provides insights into the timely and orderly expression of genes by comparing the profiles constructed for a pair of cells that are kept at different conditions, thus identifying a set of novel genes. In this review, the newest progress of SAGE's application and research is mentioned in details with its original method and principle outlined.