BACKGROUND: Recent investigations  have identified anthelminitic effects of many medicinal plants particularly from condensed tannin sources. In addition, gastrointestinal nematodes of ruminants have a negative effect on the farming industry worldwide. Objectives: The aim of the present study was  to determine the potential anthelmintic effects of Quercus robur extract on alimentary canal nematodes in naturally infected sheep by faecal egg count reduction test (EPGRT). Methods: The crude aqueous extract was prepared from Quercus robur as tannin extract. The nature and intensity of helminth infection was determined by coprological examination. The faecal samples of 600 sheep were collected from different regions of Kurdistan province. The samples were examined by flotation method (Clyton-Lane technique). Fifteen sheep with the most count in egg per gram (include Marshallagia, Nematodirus and Trichostrongylids) were divided into three groups of five animals: First group (test group) were drenched with Quercus robur extract at 3.75g/kg, second group (positive control group) received Albendazole 2.5%, orally at 5mg/kg and third group (negative control) without treatment. Results: The results of faecal examination  3 days after administration indicated significant reduction of EPG in both group’s treatment and positive control groups, 90.76% and 90.83% respectively, whereas there was no effect in the third group. Results were evaluated by Chi-square analysis and showed significant differences between treatment and negative control groups (p≤0.05). Nosignificant differences were observed between treatment group and positive control group (p≥0.05). Conclusions: Results reveal that aquatic extract of Quercus robur has anthelminitic activity and further large scale studies are suggested to confirm pharmacologic effects of this herbal extract.