The complete RNA genome sequence of Tianjin strain, isolated from marmoset, has been determined. The genome was 15,384 nucleotides (nt) in length, which was identical to that of Sendai virus (SeV), and consisted of six genes in the order 3'-NP-P/C-M-F-HN-L-5'. The gene junctions contained highly conserved transcription start and stop signal sequences and trinucleotide intergenic regions (IGR) similar to those of SeV. There was also an overlapping open reading frame and a conserved AnGn site (AAAAAGGG) in the P mRNA. Phylogenetic analysis based on protein sequences from other members of the family Paramyxoviridae showed that Tianjin strain belonged to the genus Respirovirus and was most closely related to SeV. Pairwise comparisons of amino acid identities and phylogenetic analysis with homologous sequences of known SeVs demonstrated that Tianjin strain represented a new evolutionary lineage of SeV.