Abstract RNA splicing is one of the most important events of pre-RNA maturation. Pre-RNA transcript may be spliced in several different ways, allowing a single viral gene to encode multiple proteins. The retroviral life cycle requires that significant amounts of RNA remain unspliced and perform many function in the cytoplasm. Simple retroviruses produce one single-spliced env RNA, but complex retroviruses, such as HIV, are characterized by the production of multiple-spliced RNA species. In this review we will summarize the structure of HIV genome and HIV-1 splicing mechanism. We hope that understanding the mechanism of HIV replication and identification of ancillary host factors involved in the process of HIV replication may result in discovery new therapeutic agents and may improve the knowledge of viral pathogenesis.