Toxascaris leonina adult worms live in the gastrointestinal tract of dog, cat, and fox, releasing eggs which enter the environment by the fecal route. Previously, we reported that T. leonina adult worm derived protein was able to inhibit OVA-specific Th2 responses, and in particular, immunization with parasite proteins exerts a more profound protective effect than allergen treatment. In order to gain greater insight into the relevant immune evasion mechanisms as well as basic scientific information, we have generated ESTs of T. leonina adult female worm and investigated their functions using euKaryotic Orthologous Groups (KOG) database analysis. From the randomly selected plasmids containing DNA inserts, a total of 487 reads were collected from the T. leonina adult worm cDNA library. The annotated ESTs were classified into 25 KOG categories; the most of ESTs (7.90%) were annotated with energy production and conversion, and the second highly annotated category is translation, ribosomal structure and biogenesis related ESTs (7.69%). We also identified many host-parasite immune related genes including C-type lectin, galectin, SXP, and cathepsin L-like cysteine protease coding genes. It is necessary to get more information regarding these genes for understanding about the mechanisms of immune evasion of Toxascaris.