AbstractRNA viruses are much more than DNA viruses in quantity and species in nature. It can be divided into many types of viruses according to genomic type. Recently , many researchers indicate that the ret ron existing in Myxobacteria , which carries only one reverse transcriptase gene , is the possible ancestor for all kinds of viruses , with the following evolution model : Retron →Ret roposon →Ret ransposon →Ret rovirus →Pararet rovirus →DNA viruses. It is very different between transcription/ replication of RNA virus and DNA virus genomes in many aspects. RNA-dependent RNA polymerase is the major catalyst for transcription/ replication. Initiation sites for RNA virus t ranscription/ replication are specific structures [poly (A) or tRNA] at 3′ terminal region. Internal stop results in transcription but reading through to 5′end resulting in replication. RNA viruses use the following four kinds of templates in transcription/ replication : ( + ) ssRNA template , ( - ) ssRNA template , ( + ) aRNA template , ( - ) aRNA template. The mechanism of selective regulation on RNA templates is very complex and the acknowledgements of the regulation mechanism are quite few up to now. Selecting template and the binding of transcription factors with RNA pol to form replicon are two major regulatory means. Besides promoter and transcription factors , 5′UTR and 3′UTR also regulate the transcription of RNA viruses.