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Recent studies of geothermally heated aquatic ecosystems have found widely divergent viruses with unusual morphotypes.Archaeal Viruses isolated from these hot habitats usually have double-stranded DNA genomes, linear or circular, and can infect members of the Archaea domain.In this study, the codon usage bias and dinucleotide composition in the available complete Archaeal Virus genome sequences have been investigated.It was found that there is a significant variation in codon usage bias among different Archaeal Virus species, which is mainly determined by the base composition.The outcome of correspondence analysis (COA) and Spearmans rank correlation analysis shows that codon usage of selected Archaeal Virus genes depends mainly on GC richness of genome, and the genes function, albeit with smaller effects, also contributes to codon usage in this virus.Furthermore, this investigation reveals that aromaticity of each protein is also critical in affecting codon usage bias of these viral genes although it was less important than that of the mutational bias.Finally, the relative synonymous codon usage (RSCU) of 26 genes from these 11 Archaeal Virus genomes is analyzed using a hierarchical cluster method.The result reveals that genes of genomes with similar GC content are classified into the same lineage, and gene function may play important role in determining the classification at the level of sublineage although other factors may also involve in.These conclusions not only can offer an insight into the codon usage bias of ArchaealVirus, but also may help in the gene classification of Archaeal Viruses .