Summary.We report the entire open reading frames (ORFs) sequences of four TT virus (TTV) isolates, one genotype 2 (G2) and three G4 isolates. Despite a DNA virus, TTV possesses high rate of amino acid (aa) substitution: the aa sequence homology of ORF1 and 2 is lower than the nucleotide homology. The partial N22 region of ORF1 is suitable for genotyping of prototype TTV isolates, because the phylogenetic tree from partial N22 sequence is consistent with that from the entire ORF1. Based on our sequence data, ORF2 from most isolates excluding G1 encode truncated 49aa (pORF2a) because of an in-frame stop codon, although ORF2s from most G1 isolates encode 202aa (pORF2ab). Just downstream the stop codon, another ORF encoding a protein of approximately 150aa (pORF2b) is found, whose homology is quite low among these genotypes. Our in vitro transcription/translation study supports that all G1a and a part of G1b without an in-frame stop codon dominantly encode pORF2ab, a novel 23kDa protein, whereas the other genotypes with an in-frame stop codon encode pORF2b (17kDa). Our data indicate TTV G1a and a part of G1b should have different characteristics from the other genotypes.