The envelope protein(Env) of lentiviruses such as HIV,SIV,FIV and EIAV is larger than that of other retroviruses.The Chinese EIAV attenuated vaccine is based on Env and has helped to successfully control this virus,demonstrating that envelope is crucial for vaccine.We compared Env variation of the four kinds of lentiviruses.Phylogenetic analysis showed that the evolutionary relationship of Env between HIV and SIV was the closest and they appeared to descend from a common ancestor,and the relationship of HIV and EIAV was the furthest.EIAV had the shortest Env length and the least number of potential N-linked glycosylation sites(PNGS) as well as glycosylation density compared to various immunodeficiency viruses.However,HIV had the longest Env length and the most PNGS.Moreover,the alignment of HIV and SIV showed that PNGS were primarily distributed within extracellular membrane protein gp120 rather than transmembrane gp41.It implies that the size difference among these viruses is associated with a lentivirus specific function and also the diversity of env.There are low levels of modification of glycosylation sites of Env and selection of optimal protective epitopes might be useful for development of an effective vaccine against HIV/AIDS.