The present study was carried out to determine the prevalence of gastro-intestinal nematode species of sheep in Elazığ. Gastro-intestinal tracts of 150 sheep were examined. 134 of 150 (89.33%) were found to be infected with nematodes. Twenty six nematode species were identified in sheep. A total of 63879 nematodes were collected from infected sheep. Average number of parasites for each animal was 476.71. 1-11 different species of nematodes were detected in sheep. Number of parasites per animal was 1-3223.

The nematodes most frequently observed were Marshallagia marshalli (66.67%), Ostertagia circumcincta (62.67%), O.occidentalis (42%), O.trifurcata (24.67%), Trichuris ovis (28.67%), Trichuris skrjabini (20.67%), Nematodirus abnormalis (18.67%), Teladorsagia davtiani (14%) and N.filicollis (13.33%).

The most frequently observed Marshallagia marshalli and Ostertagia species in sheep were seen in all seasons. Number of parasites in animals was high during June, July, October, November and December whereas low in all other months for Ostertagia species. For Marshallagia marshalli, number of parasites in animals was found to be low between March-September and high in rest of the months.

Trichostrongylus species were not observed during the month of February, but they were present at low numbers in other months. Nematodirus species were not present during the month of May, they were present in rest of the months and they reached the highest levels in August and October.