Morphological and genetic analyses were performed on four avian species of the subfamily Capillariinae (Nematoda: Trichuridae), i.e., Capillaria anatis from chickens (Gallus gallus domesticus) in Japan and the Philippines, Baruscapillaria obsignata from chickens and captive swans (Cygnus olor and Cygnus atratus) in Japan, Capillaria pudendotecta from captive swans in Japan, and Capillaria madseni from carrion and jungle crows (Corvus corone and Corvus macrorhynchos) in Japan. Although morphometric variations of male and female worms from different hosts and/or localities made the species identification difficult, the 18S ribosomal RNA gene (rDNA) sequences clarified their taxonomic position and phylogenetic relationships. Species of the same genus clustered robustly into a single clade in the phylogenetic tree based on the 18S rDNA, demonstrating to the extent possible the validity of the latest classification of the subfamily following Moravec's rearrangement in 1982. Male worms of C. pudendotecta are described here for the first time.