This research was carried out to determine whether adding oregano essential oil as a feed additive to the diet would affect the performance, carcass characteristics and some blood parameters of lambs. In the trial, 36 weaned male Kivircik lambs (2.5-3 month-old) were used. Lambs had an initial live weight of 22,71 +/- 0,71 kg and were divided into three groups of 12 lambs each. For the two treatment groups, Origanum vulgare essential oil was added into grower feed at the dose of 250 ppm and 500 ppm respectively. Besides this, hay was provided as roughage. Feed and water was supplied ad libitum during the trial. The first week was accepted as adaptation period and the experiment lasted for 9 weeks. The live weights and feed consumptions were measured in the beginning of the experiment and on the 14, 28, 42 and 56th days. Blood samples were collected before the morning feeding on the 0, 28 and 56th days of the experiment. All lambs were slaughtered, hot carcass weights and the weights of liver, empty stomach and empty intestine were determined at the end of the experiment. Serum concentrations of total cholesterol, triglyceride, high density lipoprotein (HDL) and low density lipoprotein (LDL) were measured using commercial kits. The final live weights were 28 +/- 0,73 kg and no differences were observed among treatments. Daily live weight gain, hot carcass weights and yields, organ weights and serum parameters were not statistically significant between groups (P>0.05). In conclusion, addition of the oregano oil had no significant effects on performance, organ weights and blood parameters of weaned lambs in this study.