[en] This study included two experiments, the first experiment was carried out in vitro to evaluate the effect of adding two levels of Lemongrass or Rosemary in ruminant rations on microbial protein synthesis using radio active sulfur S³⁵. While, the second experiment was to study the effect of Lemongrass (CC) and Rosemary (RO) as feed additives in rations of lambs on feed intake, nutrient digestibility, some parameters of blood and rumen activity. Meanwhile, body weight and economical efficiency were studied. Twenty five of Barki male lambs with average body weight of 19.8 kg ± 1 kg and 3- 4 months of age were divided into 5 similar groups (5 lambs each). The first group (control) (R1) was fed on a concentrate feed mixture (CFM) plus rice straw (RS). While, R2 and R3 were fed as R1 ration supplemented with 100 or 200 mg Lemongrass /kg LBW/d respectively. Meantime, R4 and R5 were fed as R1 ration supplemented with 100 or 200 mg Rosemary /kg LBW/d respectively.The results indicated that more microbial protein synthesis was noticed with 4 mg of Lemongrass followed by 2 mg Rosemary, 2 mg Lemongrass and control which was higher than 4 mg Rosemary/ 0.5 g concentrate mixture. The differences were not statistically significant. The dry matter intake (DMI) was not significantly different for R4 and R3 when compared with R1 (control) and it significantly decreased in R5 and R2 compared with R1. The digestibilities of DM, OM, CP, EE and NFE in the supplemented groups were not significantly differing compared with R1. The digestibility of CF was significantly increased in R2 and R4 compared with R1 and there were no significant differences for R3 and R5 compared with R1. There were no significant differences in nutritive values as TDN, DCP and SV among all supplemented groups compared with R1. Rumen liquor TVFA,s was not significantly differ at zero time, but it decreased at 3 h and 6 h with all additives compared with the control with no significant differences among all groups. The ruminal NH₃-N concentration was not significantly differing at zero time. While at 3 h the treated groups were significantly lower (p<0.05) compared with the control. At 6 h, there were significant (p<0.05) increase in R5 and R4, while decrease in R2 and R3 respectively compared with the control. The daily average body weight gain was significant for R3 and R5 being 205 and 180 g respectively compared with control (170 g). Moreover, R5, R3 and R4 were higher in feed conversion ratio compared with control. The serum cholesterol was significantly decreased (p<0.05) by adding the additives, being 54.37, 57.82, 65.43 and 67.81 mg/dl in R5, R4, R2 and R3 respectively compared with R1 (73.83 mg/dl). Feed cost/ kg gain decreased in R5, R3 and R2 being 8.43, 8.48, 8.75 L.E respectively compared with control (9.06 L.E). It could be concluded that using Lemongrass or Rosemary in rations improved microbial protein synthesis but without significant differences. Using Lemongrass or Rosemary as feed additives in diets of growing Barki sheep up to 200 mg/kg LBW may improve the average daily gain, feed conversion, and economical efficiency.