The present study was carried out to determine parasitic infection of sheep with gastrointestinal helminthes in a slaughterhouse in Fereidoonkenar city, Iran. A total number of 50 sheep were examined from April to September 2008. Nematodes were removed from abomasums, small and large intestines, and kept in A.F.A. solution (alcohol, formaldeyde, acetic acid, distilled water, and glycerine) for further diagnosis. Cestodes were removed from small intestine, washed with water, and stained with carmine acid. The results of this study indicated that 70% of examined animals were infected as follows: Ostertagia circumcincta and Marshallagia marshalli (38%), Trichostrongylus colubriformis (16%), Nematodirus spathiger (14%), Skrjabinema ovis (12%), Haemonchus contortus (10%), Camelostrongylus mentolatus (4%), and Gongylonema pulchrum, Cooperia punctata, Bunostomum trigonocephalum, Chabertia ovina (2%). Among examined animals, 14% infected with Moniezia expansa, 10% with Avitellina centripunctata and 2% with Helicometra giardi. The infection rate in younger animals was higher than in adults. The maximum infection rate was with O. circumcincta and M. marshali. No infection was found in examined rumens.