Oral stereotypes are a kind of the forms of behavioural abnormalities and many husbandry factors can cause the development of such behaviours in almost all domestic species. In this study, effects of housing based on group condition and also sex differences on the development of oral stereotypes were investigated in fattening lambs. Ten male and ten female Turkgeldi synthetic breed of lambs were used. Animals were assigned to sex groups at the beginning of the study and housed in pens that consisted of metal feed through and water buckets on a straw bedded floor during the experiment. Behavioural observations were taken by two observer and time sampling technique was used. Activities such as biting, licking and chewing of through, water bucket and also bars of pen were recorded as oral stereotypes, Generally, it was indicated that intensive group condition in fattening lambs causes the development of behavioural abnormalities related to nutritional origin. Activities towards the bedding material, standing, lying and wool chewing behaviours were significantly affected by sex. The male lambs showed more activities in standing and wool licking and wool chewing behaviours than the females while the lying and activity towards the bedding material observed more frequently in the female group. This finding indicated that general activity was high in the male lambs. There was no significant sex effect on the total oral stereotypes. It was concluded that lack of structural materials have an important role in the development of oral stereotypes. Ln addition some stressful conditions that caused by group housing may also resulted in the development of such abnormalities especially for the male lambs.