Protein arginine methyltransferases (PRMT) involved in the regulations of signal transduction, protein subcellular localization, and transcription have been mostly studied in mammals and yeast. In this study orthologues of eight human PRMT genes (PRMT1-7 and HRMT1L3) were identified in both puffer fish Fugu rubripes and zebrafish Danio rerio. The fish PRMT genes appear to be conserved with their mammalian orthologues at the levels of amino acid sequences as well as genomic structures. All vertebrate PRMT genes contain 10-16 coding exons except PRMT6 that contains only one coding exon. Western blot analyses of zebrafish tissue extracts confirmed the expression of some PRMT proteins in zebra fish. We further identified six PRMT members (PRMT1, 3-7) in an invertebrate chordate Ciona intestinalis. Genomic structures of the PRMT orthologues are no more conserved in the ascidians, as PRMT3 and PRMT5 contain only one coding exon while PRMT6 contains six exons. PRMT2 and HRMT1L3 that are missing in Ciona appear to be vertebrate-specific. HRMT1L3 is a PRMT1 paralogue with highly conserved sequences and exact exon junctions, whereas the PRMT2 orthologues are very diverged. Different PRMT orthologues are likely to evolve at different rates and the PRMT1 orthologues appear to be most conserved through evolution. Furthermore, phylogenetic analyses using the core regions of various PRMT genes show that PRMT5 with the type II PRMT activity is separated in one branch. All other PRMT genes including PRMT1, 2, 3, 4, 6, 7 and HRMT1L3 clustered in the other branch, probably represent the genes for the type I activity.