Eighteen growing Ossimi lambs (28.92 kg average live body weight and 6-7 months old) were used to evaluate incorporating thyme essential oil (TEO) in ration on nutrients digestibility and growth performance. In growth trial lasted 90 days followed by digestibility trial for 14 days, the lambs were randomly divided according to their live body weight into three feeding groups (6 each).Total mixed ration consisted of 60% concentrate: 40% roughage was offered to lambs in all groups to cover its total requirements. Whereas, there was no TEO in the control feeding group, R1, while R2 and R3 were supplemented with 0.1 and 0.2 TEO from DM intake, respectively. Data of nutrients digestibility indicated that incorporating TEO in both of R2 and R3 significantly (P<0.05) increased digestibility of DM, OM, CP, EE and NFE. While, EE digestibility was only significantly (P<0.05) increased in R3 compared with R1. The same trend was observed for nutritive value either as TDN or DCP, whereas it was significantly (P<0.05) improved with R2 and R3 compared with R1.There were no adverse effects for thyme oil supplementation on rumen pH, but significant (P<0.05) decreased rumen ammonia concentration and increased the rumen volatile fatty acids compared with control group. As a result of this improvement in nutritive value, the highest body weight gains were recorded with R2 and R3 (187 and 200 g/h/d) compared to 160 g/h/d. for R1. So, it can be concluded that incorporating thyme essential oil in growing lambs ration by either 0.1 or 0.2% from DM intake improved both of nutrients digestibility and growth performance.