Adults of the large intestinal nematode, Ascarida galli were obtained from domestic chickens, Gallus gallus domesticus. Specimens were divided for light and scanning electron microscopic preparation. Light microscopy was used to confirm the species. The largest nematode of domestic chickens had a prevalence of 40% in Chiang Mai Province. In the gastrointestinal tracts then were recovered from the duodenum, jejunum and ileum.

The body length of the males ranged from 3.56 to 7.35 cm. and from 5.50 to 9.65 cm. of females. The unique characteristic observed by light microscope was 3 equal large lips at the head end. SEM observations revaled more detail : 1 dorsal and 2 ventrolateral lips with sensory organs. The dorsal lip was composed of 2 labial pores and 2 cephalic pores.

Each of the ventrolateral lips was composeed of labial pores, 1 amphid, 1 cephalic pore and 1 ciliated sensory papillae.

The cuticular surface was transversely striated excepted for the lips. The male and female differed at the posterior part of the body. The male had a large preanal sucker, caudal alae and anal papillae. The female had the anus near the posterior part of the body.